Added residues property to biothings:Assembly class
biocodegff.get_gff3_features() now populates residues and length attributes of Assembly features.
added translation table 1 and translate() function
added get_residues() method to CDS features
Properly handles getting residues for CDS on the -1 strand
biocodeutils.translate() now inserts an X and prints a warning when unknown codon is encountered.  (previously raised an exception)
First version, tested by cmcracken
Merge branch 'master' of github.com:jorvis/biocode