Provide access to git ref information to templating engine

Allow for a user to reference the git commit hash within a template. Example:

#
# Cookbook Name:: |{ cookbook['name'] }|
# Recipe :: |{ options['name'] }|
# Template Pack Version :: |{ git['ref'] }|
# 
# Copyright |{ cookbook['year'] }|, Rackspace
#

Having access to other git information such as branch may also be useful.

The use case here is to allow any person to determine what version of a shared template pack was used to generate a given recipe or set of recipes. This would be used in cases where additional stencils are leveraged to expand an existing aged environment. Newer versions of stencils may have different cookbook dependencies or logic tying the components together which would force a person to overhaul the entire cookbook in order to get things converging.

rackerlabs / fastfood

Provide access to git ref information to templating engine #34