Release notes for 0.6.0 (GA)

Release notes for 0.6.0, against 0.6.0-rc.1 .

Incorporates (offline) feedback from @aledsage on https://github.com/brooklyncentral/brooklyn/pull/980 (same PR against master)

![0 6 0 release notes](https://f.cloud.github.com/assets/879000/1406778/4afcd3d6-3d5a-11e3-9224-6b0f3c1e23bc.png)