Interface development

[brnorris03]

For git commit stats, implement something like the following interface:

cloneRepos -- take a file containing a list of URLs and clone them locally unless they have already been cloned

getStats -- for a list of repos, compute stats at the indicated granularity (one of the parameters can be used for that, e.g., daily, every n days, monthly, etc.); this means that a stats data structure needs to be designed, as well.

[jprideaux]

I created a new class (GitCommand) with some functions for cloning, getting versions, and extracting commit data. A lot more can be added to it, butI think this is a good starting point.