Add rcm

The rcm suite of tools are used to manage dotfiles. They can symlink
dotfiles from a repo into your homedir, turn an existing configuration
file into a symlinked dotfile, and in general make it easy to try new
dotfile repos.
Use thoughtbot/rcm for Homebrew

Back when rcm was an experiment by Mike Burns, the `homebrew-rcm` GitHub
repo was hosted under the `mike-burns` account. It has since been moved
to `thoughtbot` so that more may share in the love.
Change Homebrew install path

Looks like it's hosted in a different repository now.
Add command for accepting XCode agreement on Mavericks
Upgrade Ruby to 2.1.0
Remove initdb, fixes #182

The latest Homebrew formula runs this as part of post-install.