- 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