[Virtio-msg] RFC status

All,

The RFC went out a bit ago. I updated it based on Bertrand's and Arnaud's suggestions (cover letter, commit description, and s/request/requests/ only). (I also fixed a s/massage/message/ in the cover letter.)

Going forward the new baseline for spec work will be virtio-msg-rfc1. This branch is now the default at the linaro repo [1]. Please target all new pull requests to this branch.

The virtio-msg-alpha branch is now frozen but will be kept for reference.

Thanks, Bill

[1] https://github.com/Linaro/virtio-msg-spec