Created a DSC Resource for keeping Git repository in sync

Written this to keep a local git repository in sync with a remote repository. Planning to use for dev/test environment. 
Looks like this resource completely ignores the `Ensure` parameter, always behaving as though it's set to Present.  If there's not going to be any logic around an `Ensure` value of Absent, it's fine to just take this parameter out of the resource.  It exists in most resources, but is not strictly required by DSC.