Simplify count_words, add trim_and_count_words

The original count_words function (before it was put into utils::) also trimmed
comments. For compatibility this behaviour was retained at first. However, due
to the name the trimming is not immediatly apparent and many times not
wanted.

Therefore, this commit replaces count_words with an implementation that
just does what it says. If a comment should be trimmed there is a
trim_comment function. For convenience, a trim_and_count_words function was
added and is now used where the old behaviour was needed.