Fix Gruntfile to look at local Jasmine

Couldn't get the tests to run without this
Add initial tests for GetReferences
Implement first pass at getReferences
:lipstick:
Add more test cases

We'll now do a better job matching remote and tag references
getReferences now returns local, remote, and tag references
Mention getReferences() in the README
Support checking out branches

This includes the ability to create new branches
Update tests to support checkoutReference
Update docs
Add cstring for strncmp support in Travis
Add git_reference_free call when looking up a reference
Add git_reference_free call after creating a branch
:lipstick:
Ensure that the first parameter starts with "refs/heads/"
:lipstick:

Most of these have to do with:
* rearranging variables
* cleaning up memory after `git_` function calls
* removes excess curlies
Support shortRefName in checkoutReference

Users can pass in `.checkoutReference('new_branch')` instead of
`.checkoutReference('refs/heads/new_branch')
Merge pull request #5 from atom/add-get-references

Implement branch manipulation