Use the Editor for Commit Messages

Stop doing quick one-liners and put a bit of thought into my commit
messages.
Remove DelimitMate Plugin

I like it, and it emulated TextMate when I switched to Vim, which
brought me comfort, but it's time to put it to rest:

* It doesn't ingegrate well will repeating (the additional quotes and
  such aren't included in the repeated command)
* It just as often included extra closing quotes when I didn't want them
Display Diff When Entering Commit Message

This will help double-check I'm committing what I think I'm committing.
Include Dash Integration into Vim

Use `:Dash` to search for the word under the cursor or `:Dash keyword`
to search for 'keyword'.