* configuration-overrides:
  Add a way to override .gitconfig and update README

Currently only works with 2 digits season and episode numbers. Also doesn't work
with multi-episode files.

The Markdown b:ml_commentstring was being overwritten because the
Markdown plugin includes the HTML plugin.

Also change the Markdown syntax override to include the ghmarkdown
syntax plugin instead of being a symlink to it.

Also deleted some FileType specific settings that aren't needed anymore.