doc update
added UTR support for counting 5/3 UTRs as part of stats
only look for UTRs if they are present
keep exon count for things w/o CDS
rev- regions for coding, utrs
mitochondrial chrom could also be named 'M'
key error
better cds handling for stats
syntax
syntax2
key errors
added -startonly option for counting
typo
added excluderef filter - eg remove chrM
migrate get_tag to return a tuple - let the calling function figure out what to do with the is-reverse oriented tags