TODO

2017.04.27:
v Move function to autoload (2017.04.29)
v Make mapping user-editable (2017.04.29)
v Add README (2017.04.29)
v Add license (2017.04.29)
v Add docs (2017.04.29)
v Add if-loaded ceremony (2017.04.29)
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:
v Fix matcher (2017.04.29)