Merge branch 'darwin' into merge-darwin
port to ubuntu:

Create symbolic links:
* .Xmodmap
* .zshrc.linux
* .fonts
Add role linuxbrew
Install dependent packages via apt
Add dependency to rake
Install as many packages as possible via Linuxbrew
loginshell supports Linux
Add Linuxbrew's zsh path
Set variable user to ENV['USER']
Remove role dependencies
Merge site-ubuntu.yml into site.yml
Merge into var/common.yml
Merge variable dotfiles
Remove ubuntu.yml
Add role brew
Fix linuxbrew path
Merge role homebrew into brew
Merge into common.yml
Install fonts manually on Darwin
Remove site-darwin.yml