Rake task namespace to backup your project

Three new options:

bk_remote - Your remote backup repo name `git remote add ...`
bk_repo - Your remote backup repo url
bk_branch - Your remote backup branch
Two rake tasks under the `backup` namespace:

Two new tasks under the `backup` namespace:

config
Creates the the remote given the options listed in your Rakefile

push
Adds, commits and pushes any changes to your backup repository