remove rawgithub; add test report summary; TODO stuff

I may have been abusing rawgithub. I was their #3 top referrer today
with 68 hits (mostly from browserstack.com). So I removed the links
from the README, and made a TODO entry for hosting the tests, docs,
and benchmarks.

A good number of browsers handle _tree tests just fine. Many more fail
at immutability. Pretty much everything on IE[789] is broken.