Configure Macvim as the standard git mergetool

Why use something else than Macvim with fugitive.vim as a mergetool?
Merge pull request #230 from treppo/patch-1

Configure Macvim as the standard git mergetool
Removed vim-slim submodule
Merge pull request #231 from andyattebery/master

Removed vim-slim submodule
Merge branch 'master' into customizations

* master:
  Removed vim-slim submodule
  Configure Macvim as the standard git mergetool