Implemented getTranscriptByStableId method in genome.py
Added test for getTranscriptByStableId
Added a Gene property and _get_gene method to the Transcript class in region.py
Minor fix to _get_gene method of Transcript class in region.py. Should test before commiting!
Minor fix to getTranscriptByStableId in genome.py and more comprehensive tests in test_genome.py.
Merge pull request #22 from gawbul/master

Implemented a getTranscriptByStableId method in response to issue #21