add min_read_length to ALGORITHM_KEYS
Remove B run  trimming.
Finalize removal of old brun trimming: removes supplemental code that is no longer used. Plug min_read_length into read_through_trimming. Add documentation. #267

Conflicts:
	HISTORY.md
	bcbio/bam/trim.py
	setup.py
Merge remote-tracking branch 'origin/tuxedo' into tuxedo