Integrate MRT Table Dump (RFC 6396) into BIRD

Asynchronous periodic mrt table dumps of routes configuration in bird.conf:
mrtdump routes {
  [ filename "<format>"; ]
  [ table <name>|"<wildcard name>"; ]
  [ period <num>; ]
  [ filter <filter>|where <condition>; ]
}

Synchronous mrt table dumps of routes in BIRD client:
mrtdump routes [table <name>|"<wildcard name>"] [to "<filename format>"] [filter <filter>|where <condition>]