Enable readthedocs build for 0.1.0.1

The release-0_1 branch corresponds to the gmxapi 0.1.0.1 PyPI release, but does not build on readthedocs. This is probably resolved most easily by adding a special conf.py and static html content that rtd can use for the 0.1.0.1 version. If documentation bug fixes are applied to GROMACS 2020, this content would need to be updated, but it should be a low maintenance issue.