Checking out a repo, finding the slides, and returning the slide names

... except since node is all async, it's happening asynchronusly.
There's a trick here, I'm sure; this virtual method is expecting
something synchronous. Perhaps exec has a way to work sychronously?
Whatever. That's well out of my depth.
Merge pull request #21 from matthoffman/read-from-git

WIP:  getting slides from git