Linton

This release makes nancy errors more legible.

Fix the tests and tweak Markdown output not to have an (extra) trailing newline.

This release switches to CommonMark, using the mistletoe Python CommonMark implementation, so the defaults are now pure Python.

This release adds a `--force` option to `linton init`, to allow existing sites to be updated.

This release fixes the `menudirectory.in.py` script, which was broken.

This release fixes some permissions of files installed by the `init` command, and updates the syntax of some commands in the documentation (not user-visible).