Added GeneModel class
Changed tool.py to tools.py
Documentation changes
Updated genomic_coordinate to use Interval class
New gene model captures Gene, Transcript and Exon
Fixed genomic_coordinate comparisons
Removed obsolete Range class from binf.sequence
Added tests for argsort
Added key argument to argsort
Fixed initial sorting in nested_containment_list
Added ncl based model set
nested containment list removed redundant intervals