Improve project organization, and document it better

Proposed improvements to project organization and docs.

* the 5 first patches are form, but don't change the actual rules
* 1 patch is carried from @erikh, and reflects the new docs-first proposal system
* 1abffc6 is a major upgrade of the project structure, with a strawman for a new, centralized MAINTAINERS file.

Feedback welcome!
Not a big fan of the format here -- what's the rationale for it being so complex?  I like the extra information, but it's not very easy to read and seems like it's going to be very error-prone to update unless we've got tooling verifying correctness.