py-alabaster: updated to 0.7.13

0.7.13

:support:`- backported` Modernized the project: s/Travis/Circle/ for CI, README badges, setup.cfg removal, metadata refresh, etc.

:support:`- backported` Dropped support for Python 2 and Python <3.6. This includes various minor updates to work correctly with modern versions of Sphinx (1.6 at the very least). Thanks to Adam Turner for a pile of patches here.

Warning

This change is backwards incompatible if you're on an old Python version.

:support:`- backported` Tweak CSS somewhat for compatibility with modern Sphinx versions' base stylesheet.

(adam)