WIP: Release timeline for 2.15.1, 2.16. and 2.17

[Carlos O'Donell]

I've started the process of planning the releases here:

http://sourceware.org/glibc/wiki/Glibc%20Timeline

My next step is:

* Cleanup `Realease' process here:
http://sourceware.org/glibc/wiki/Release

I would like the release process to be uniform for major or minor, it
shouldn't matter.

* Rejigger the planning dates after smoothing out the release process
instructions.

* Seek community feedback.

I'm posting this here so anyone can follow along and comment (if you
aren't already subscribed to the wiki changes).

Cheers,
Carlos.