pyenv over homebrew python

Given that you're using rbenv, I was wondering why you're not using pyenv? I've found it to be invaluable especially working back and forth between python 2 and 3 pretty extensively. After all, we should all be starting new projects in python 3, right?

The source code is well maintained and nearly identical to rbenv. The rbenv HEAD is even merged in periodically.

The installation is entirely identical with the exception that python-build (like `ruby-build`) is included in the pyenv package :)

```
brew install pyenv
brew install pyenv-virtualenvwrapper # not necessary, but a nicety
pyenv install -l # list python versions
pyenv install 2.7.10
pyenv install 3.5.0
pyenv global 2.7.10 3.5.0 # sets global python2 and python3
```

Please let me know if you'd like me to submit a PR!

P.S. Love the repository, I've been trying to maintain a similar repo: https://github.com/AlJohri/dotfiles/blob/gh-pages/Brewfile
You should consider using the `brew bundle` command instead of `brew.sh`. (its pretty new, released within the last year).