Adding neovim formula for Homebrew
Adding `make` step
Fixed nvim homebrew formula

I now also do make install
homebrew: deparallelize build
Removed testing for Homebrew installs

Fixes the luarocks/busted error.  Homebrew isn't exactly being
facilitated, so it's not an ideal solution, but it works.
Homebrew formula builds dependencies through make

This way, if the dependencies change, and the install process needs to
change to accommodate this, the Homebrew formula won't need revising.
neovim.rb: modernize the style

https://github.com/styleguide/ruby
neovim.rb: improve dependency

1. remove unnecessary deps `md5sha1sum`
2. add `=> :build`
3. add missing deps `autoconf`
homebrew: use Makefile-defined defaults. #1259

Assuming homebrew always uses a clean workspace, a separate "cmake" step
is not necessary.
homebrew: fix install prefix
homebrew: look for .git/ outside of build workspace #1274
Homebrew: Compile as release build.
Homebrew: let Homebrew handle external resources download
README: add install instructions
Merge pull request #2 from xu-cheng/relocate-formula

Homebrew: move formula to neovim/homebrew-neovim