Swap READMEs to markdown

Suggested by vapier@ in I7daf1cbe93f8809e469698d7772a6c68baf9e194

This ignores README.chromium, since I'm unsure if that's a special name
that some tool somewhere relies on.

I skimmed over all of these in gitiles (as you can probably tell by the
35 patch sets :) ) and fixed the issues that jumped out at me. I'm sure
that some remain somewhere, but I think I got the majority of them.

An attempt has been made to make all files roughly follow the rules
here:
https://github.com/google/styleguide/blob/gh-pages/docguide/style.md

Note that not all of them have super meaningful introductions with
ToCs/etc, but the rest should be relatively consistent with that guide.

BUG=None
TEST=Manual inspection

Change-Id: I158048d972d49966e3b8ff1e07e5429928edb339
Reviewed-on: https://chromium-review.googlesource.com/1504893
Commit-Ready: George Burgess <gbiv@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
24 files changed