Remove Unite.vim.  Completely replaced by vim-niffler.

- I'm finally parting ways with Unite.  As mentioned in earlier commit messages,
  it's a great idea but just not for me.  The plugin was too heavy, too buggy,
  and too slow.  It was fairly poor at it's main purpose (for me at least) of
  fuzzy file finding.  Niffler is fast and I'll be able to improve it to fit my
  workflow as I see fit.
Configure Niffler. Change base mapping from 'gh' to 'zn'
Add gb mapping to change buffers