Brewfile

There's a [large demand](https://www.google.com/search?btnG=1&pws=0&q=%22brewfile%22+%7C%7C+%22brewdle%22#pws=0&q=%22brewfile%22+%7C%7C+%22brewdler%22) for Brewfile integration, an [incredibly popular use-case[(https://github.com/mathiasbynens/dotfiles/blob/master/.brew), and there are tons of people using the Ruby niche [Brewdler](https://rubygems.org/gems/brewdler). It's even been asked for in our GitHub issues (#16664 & #5250), so I thought I'd make a pull request.

It's written so that `brew install` (like `npm install` or `bundle`) without any arguments searches for and uses a Brewfile (optional case), which would look like:

```
hub
node
spark
```

It also uses the Brewfile for `brew uninstall` without arguments, so that Homebrew dependencies can be shared quickly and easily with projects. Let me know if you have any concerns with this pull request that I can address. I found it useful today and thought the community might enjoy it.