JSON changes for upcoming 0.2.0 release

This update:

* Bumps the version to 0.2.0-SNAPSHOT.
* Makes JSON keys keywords by default in `body-params`.
* Adds deprecation notices to the CHANGELOG.md for the Cheshire switch.

If these seem reasonable @timewald, go ahead and merge this.

I'd really like to get #92 done for 0.2.0 as well. I'm going to put a call out for any more breaking changes we want to put into 0.2.0.