propose adding headers to RFC template

[gitaaron]

I propose adding three fields to the header of our RFC template -

Status: [Draft|Final|Implemented|Inactive]
Authors: [Full names|github nicknames]
Reviewers:  [Full names|github nicknames]

Status will give the reader an idea of where the RFC is at in the in roadmap.
Authors/reviewers will tell the reader who they can contact if they have questions.