Make it easy to deploy the current git branch

[dentarg]

How to use it:

# Capfile
require 'capistrano/twingly/current_git_branch'

# config/deploy/production.rb
set :branch, Twingly::Git.current_branch

In action:

$ bundle exec cap staging deploy
Deploying branch master to stage staging
...

[dentarg]

@jage Can we merge this?

[jage]

Yes, looks good!