Fix order of index methods
Merge pull request #5081 from jtratner/fix-order-of-index-methods

CLN: Fix order of index methods.
EHN: Allow load_data to load the "Titanic" and other problematic R datasets
TST: Move tests from rpy/common.py to rpy/tests/test_common.py
TST: Add tests to demonstrate the enhancements made to rpy/common.py.
DOC: Add explanation to doc/source/release.rst and doc/source/v0.13.0.txt