TODO

2017.04.27:
v Move function to autoload (2017.04.29)
- Make mapping user-editable
- Add README
- Add license
- Add docs
- Add if-loaded ceremony
v Check to see if this conflicts with existing gitcommit ftplugins (2017.04.29)
v Include the commit header in the "extra text" of the popup menu (see
  :h complete-items) (2017.04.29)

2017.04.29:
- Fix matcher