MAINT: collected the inspect calls together
MAINT: bypass inspect in stats.distributions by using explicit shapes
DOC: removed inconsistencies between shape parameters in docstrings.
MAINT: small refactoring. pep8 compliance, more robust tests
DOC: document the changes to the shapes parameter.
TST: add tests for subclassing stats.rv_continuous.
TST: tests for check for *args & **kwds w/inspected shapes
MAINT: attach _parse_args to the instance, not class.

Fixes the test failure in statsmodels induced by this PR/2588.
Attaching to the instance a kind of makes sense since
shapes/numargs are only created in __init__ anyway.