Various updates and fixes to docs

Notable addition would be the "Give us a heads up" section asking devs to email us before starting a new IA, The idea being we'd like to know what's coming earlier so we can prevent people from wasting time. I imagine once the IA pages are finished there will be room to improve the process for handling IA's at the idea stage. I know @russellholt has many thoughts on that.

//cc @zekiel @mwmiller @jagtalon @jdorweiler