Exported the GAE Context from Goon. (Fix #37)

Exported the Context from Goon type, which will fix #37

Admittedly I had issues running the tests, I kept getting errors with gae falling over saying 'too many files open'.

That being said, it all compiles, and testing it against my local development, it's looking good.
Not sure what else to add here so I can get my pull request merged? Looks like the context is already documented by the doc on the Struct type, no?