Additional doc-blocks and features for Heat

Hi @ycombinator,

As I mentioned over on https://github.com/rackspace/php-opencloud/pull/314, I had some unmerged changes from a very old fork that I was rebasing when I noticed your PR over there. I'd like to collaborate if possible to increase the feature and test coverage for Heat.

If you're on IRC, I'm idling in #heat and #rackspace on freenode (same nick as github)