Support paired-end mode for SAM format. Fix several potential bugs.

  void ReduceCandidatesForPairedEndRead(const std::vector<Candidate> &positive_candidates1, const std::vector<Candidate> &negative_candidates1, const std::vector<Candidate> &positive_candidates2, const std::vector<Candidate> &negative_candidates2, std::vector<Candidate> *filtered_positive_candidates1, std::vector<Candidate> *filtered_negative_candidates1, std::vector<Candidate> *filtered_positive_candidates2, std::vector<Candidate> *filtered_negative_candidates2);

  void GenerateBestMappingsForPairedEndReadOnOneDirection(Direction first_read_direction, uint32_t pair_index, int num_candidates1, int min_num_errors1, int num_best_mappings1, int second_min_num_errors1, int num_second_best_mappings1, const SequenceBatch &read_batch1, const std::vector<std::pair<int, uint64_t> > &mappings1, int num_candidates2, int min_num_errors2, int num_best_mappings2, int second_min_num_errors2, int num_second_best_mappings2, const SequenceBatch &read_batch2, const SequenceBatch &reference, const std::vector<std::pair<int, uint64_t> > &mappings2, std::vector<std::pair<uint32_t, uint32_t> > *best_mappings, int *min_sum_errors, int *num_best_mappings, int *second_min_sum_errors, int *num_second_best_mappings);

  void RecalibrateBestMappingsForPairedEndReadOnOneDirection(Direction first_read_direction, uint32_t pair_index, int min_sum_errors, int second_min_sum_errors, int min_num_errors1, int num_best_mappings1, int second_min_num_errors1, int num_second_best_mappings1, const SequenceBatch &read_batch1, const std::vector<std::pair<int, uint64_t> > &mappings1, int min_num_errors2, int num_best_mappings2, int second_min_num_errors2, int num_second_best_mappings2, const SequenceBatch &read_batch2, const SequenceBatch &reference, const std::vector<std::pair<int, uint64_t> > &mappings2, const std::vector<std::pair<uint32_t, uint32_t> > &edit_best_mappings, std::vector<std::pair<uint32_t, uint32_t> > *best_mappings, int *best_alignment_score, int *num_best_mappings, int *second_best_alignment_score, int *num_second_best_mappings);

  void ProcessBestMappingsForPairedEndReadOnOneDirection(Direction first_read_direction, uint32_t pair_index, uint8_t mapq, int num_candidates1, uint32_t repetitive_seed_length1, int min_num_errors1, int num_best_mappings1, int second_min_num_errors1, int num_second_best_mappings1, const SequenceBatch &read_batch1, const std::vector<std::pair<int, uint64_t> > &mappings1, int num_candidates2, uint32_t repetitive_seed_length2, int min_num_errors2, int num_best_mappings2, int second_min_num_errors2, int num_second_best_mappings2, const SequenceBatch &read_batch2, const SequenceBatch &reference, const SequenceBatch &barcode_batch, const std::vector<int> &best_mapping_indices, const std::vector<std::pair<int, uint64_t> > &mappings2, const std::vector<std::pair<uint32_t, uint32_t> > &best_mappings, int min_sum_errors, int num_best_mappings, int second_min_sum_errors, int num_second_best_mappings, int *best_mapping_index, int *num_best_mappings_reported, std::vector<std::vector<MappingRecord> > *mappings_on_diff_ref_seqs);

  void GenerateBestMappingsForPairedEndRead(uint32_t pair_index, int num_positive_candidates1, int num_negative_candidates1, uint32_t repetitive_seed_length1, int min_num_errors1, int num_best_mappings1, int second_min_num_errors1, int num_second_best_mappings1, const SequenceBatch &read_batch1, const std::vector<std::pair<int, uint64_t> > &positive_mappings1, const std::vector<std::pair<int, uint64_t> > &negative_mappings1, int num_positive_candidates2, int num_negative_candidates2, uint32_t repetitive_seed_length2, int min_num_errors2, int num_best_mappings2, int second_min_num_errors2, int num_second_best_mappings2, const SequenceBatch &read_batch2, const SequenceBatch &reference, const SequenceBatch &barcode_batch, const std::vector<std::pair<int, uint64_t> > &positive_mappings2, const std::vector<std::pair<int, uint64_t> > &negative_mappings2, std::vector<int> *best_mapping_indices, std::mt19937 *generator, std::vector<std::pair<uint32_t, uint32_t> > *F1R2_best_mappings, std::vector<std::pair<uint32_t, uint32_t> > *F2R1_best_mappings, int *min_sum_errors, int *num_best_mappings, int *second_min_sum_errors, int *num_second_best_mappings, std::vector<std::vector<MappingRecord> > *mappings_on_diff_ref_seqs);

  void ProcessBestMappingsForPairedEndReadOnOneDirection(Direction first_read_direction, uint32_t pair_index, uint8_t mapq, int num_candidates1, uint32_t repetitive_seed_length1, int min_num_errors1, int num_best_mappings1, int second_min_num_errors1, int num_second_best_mappings1, const SequenceBatch &read_batch1, const std::vector<std::pair<int, uint64_t> > &mappings1, const std::vector<int> &split_sites1, int num_candidates2, uint32_t repetitive_seed_length2, int min_num_errors2, int num_best_mappings2, int second_min_num_errors2, int num_second_best_mappings2, const SequenceBatch &read_batch2, const SequenceBatch &reference, const SequenceBatch &barcode_batch, const std::vector<int> &best_mapping_indices, const std::vector<std::pair<int, uint64_t> > &mappings2, const std::vector<int> &split_sites2, const std::vector<std::pair<uint32_t, uint32_t> > &best_mappings, int min_sum_errors, int num_best_mappings, int second_min_sum_errors, int num_second_best_mappings, int *best_mapping_index, int *num_best_mappings_reported, std::vector<std::vector<MappingRecord> > *mappings_on_diff_ref_seqs);

  void GenerateBestMappingsForPairedEndRead(uint32_t pair_index, int num_positive_candidates1, int num_negative_candidates1, uint32_t repetitive_seed_length1, int min_num_errors1, int num_best_mappings1, int second_min_num_errors1, int num_second_best_mappings1, const SequenceBatch &read_batch1, const std::vector<std::pair<int, uint64_t> > &positive_mappings1, const std::vector<int> &positive_split_sites1, const std::vector<std::pair<int, uint64_t> > &negative_mappings1, const std::vector<int> &negative_split_sites1, int num_positive_candidates2, int num_negative_candidates2, uint32_t repetitive_seed_length2, int min_num_errors2, int num_best_mappings2, int second_min_num_errors2, int num_second_best_mappings2, const SequenceBatch &read_batch2, const SequenceBatch &reference, const SequenceBatch &barcode_batch, const std::vector<std::pair<int, uint64_t> > &positive_mappings2, const std::vector<int> &positive_split_sites2, const std::vector<std::pair<int, uint64_t> > &negative_mappings2, const std::vector<int> &negative_split_sites2, std::vector<int> *best_mapping_indices, std::mt19937 *generator, std::vector<std::pair<uint32_t, uint32_t> > *F1R2_best_mappings, std::vector<std::pair<uint32_t, uint32_t> > *F2R1_best_mappings, int *min_sum_errors, int *num_best_mappings, int *second_min_sum_errors, int *num_second_best_mappings, std::vector<std::vector<MappingRecord> > *mappings_on_diff_ref_seqs);

  void EmplaceBackMappingRecord(uint32_t read_id, uint32_t barcode, uint32_t fragment_start_position, uint16_t fragment_length, uint8_t mapq, uint8_t direction, uint8_t is_unique, uint8_t num_dups, uint16_t positive_alignment_length, uint16_t negative_alignment_length, std::vector<MappingRecord> *mappings_on_diff_ref_seqs);

  void EmplaceBackMappingRecord(uint32_t read_id, const char *read1_name, const char *read2_name, uint16_t read1_length, uint16_t read2_length, uint32_t barcode, uint32_t fragment_start_position, uint16_t fragment_length, uint8_t mapq1, uint8_t mapq2, uint8_t direction, uint8_t is_unique, uint8_t num_dups, uint16_t positive_alignment_length, uint16_t negative_alignment_length, std::vector<MappingRecord> *mappings_on_diff_ref_seqs);

  void ApplyTn5ShiftOnPairedEndMapping(uint32_t num_reference_sequences, std::vector<std::vector<MappingRecord> > *mappings);