formatters: Remove Hoedown formatter, split it off to a pluging. Its availability was spotty depending on the platform (because `misaka` doesn't have binaries available for even Windows, for instance). So it was split off to a plugin that the user can install if needed.

*.pyc
*.egg-info
.cache
__pycache__
venv
tags
bower_components
node_modules
build/lib
util/messages/_cache
util/messages/_counter
dist
docs/_cache
docs/_counter
foodtruck/static
piecrust.egg-info
piecrust/__version__.py
.ropeproject