reformatting test cases, replacing 'ok' tests with 'is'
spliced_seq method in Transcript can have soft_mask argument
if specified, will return sequence with lower cased UTRs
get_all_Introns method also available on gene level
test reformatting, replacing a number of ok tests with is
added tests for get_all_Genes_by_source, is_chromosome, has_karyotype, karyotype_rank and forced expand methods
_mask_features method expanded to allow masking of non-repeat features
will now mask for any list of features provided