Speed up MacVim with Lua

It's always a good idea to install MacVim with Lua support. Homebrew does not compile with Lua support by default. This gets you the benefit of a noticeably-faster Unite.vim.

brew install macvim --with-cscope --with-lua --override-system-vim --with-luajit --with-python3

Also, the option --override-system-vim will allow you to use vim in the command line apart from the GUI... also a great idea!