lots of gyp infra clean up

[Dirk Pranke]

Hi all,

The infra and cleanup work I've been doing on GYP is now mostly done:

We have a new project site w/ freshened-up documentation:

https://gyp.gsrc.io/

This is derived from markdown documents stored in-tree (on the md-pages branch of the git repo), and served via

Gitiles' markdown renderer (the same system that is powering the source viewer at https://chromium.googlesource.com/external/gyp ).

We have new buildbots:

https://build.chromium.org/p/client.gyp/waterfall

There are tryservers and continuous builders.  They're even green!

You can now even clone the repo using `fetch gyp`, just like other chromium-related projects.

Hopefully this is helpful. Updating the docs is just like updating code, except that you should branch off of refs/origin/md-pages

instead of refs/origin/master (this uses the same basic approach that GitHub does w/ github.io).

Feedback welcome!

-- Dirk