Added nodeGitApi.

Defined the nodeGitApi to be a wrapper around nodegit.
Added a function to retreive a commit by sha.
Added an internal class: GitApiCommit.
Added a skeleton for GitApiCommit.getTestCount.
Added a test case for the retrieval of the number of test cases in a repo.
Merge remote-tracking branch 'origin/master'

Conflicts:
	spec/samplespec.js