v0.2

• added unit tests
• renamed GeneMatrixTransposed to GeneSets
• renamed GeneSets.all_identifiers to GeneSets.all_genes
• GeneSets, GeneSet and ExpressionSet now support len() and repr()
• added GeneSets.gene_sets_by_name
• added GeneSets.to_frame() which converts the gene sets to binary membership DataFrame
• GeneSets constructor will now warn if redundant gene sets (which may influence the results) are detected