Switch to using json from the stdlib.

This library previously used the oauth2client `anyjson` wrapper (which existed
to handle backwards compatibility with python 2.5. Given that boto doesn't
support 2.5 anymore, this seems unnecessary (and `anyjson` has disappeared
from oauth2client).

(Also fix the formatting in one line of `README.md`, and add a `.gitignore` file.)
Merge pull request #11 from craigcitro/anyjson

Switch to using json from the stdlib.