Gwsumm

Packaging and documentation point release, including:

* Use a theme with a bootstrap navigation bar for documentation, styled consistently with the pages for [hveto](http://hveto.readthedocs.io) and [gwdetchar](http://gwdetchar.readthedocs.io)
* Add conda-forge badge to README.rst

This release introduces no functional changes relative the previous one. For full changes see https://github.com/gwpy/gwsumm/compare/0.1.1..0.1.2.

Bugfix release for GWSumm, including:

* Update a reference to a function that's been moved upstream (252)
* Update CSS stylesheets now that we use gwdetchar to build HTML (252)
* Sundry python-3.7 compliance fixes (252, 253, 254)
* Explicitly support python-3.7 (252)

This release introduces no functional changes relative the previous one. For full changes, please see https://github.com/gwpy/gwsumm/compare/0.1.0..0.1.1

This is the first release of gwsumm - a python toolbox used by the LIGO Scientific Collaboration for detector characterization