Cut a release

[choldgraf]

• Ensure that the Sphinx-Togglebutton version number
  is correct, and remove the dev0 part of the version number.
  Make a PR with the new number and merge into master.
• Create a new distribution for Sphinx-Togglebutton by
  following the twine release instructions
• Confirm that the new version of Sphinx-Togglebutton is posted to pypi
• Bump the Sphinx-Togglebutton version number to
  the next minor (or major) release and append dev0 to the end.
• Celebrate! You've just released a new version of Sphinx-Togglebutton!