Implement lots of tinyquery functions

Summary:
There are a few hacks here:
-NTH and QUANTILES should handle repeated fields in their type
validation/detection. Instead, I cheat and say they return ints.
-NTH and QUANTILES should take constants, not expressions, so that we don't get
a whole column of constants when evaluating them.
-I just added a stub for stddev_samp.

Still, this is enough to make the BigBingo fast end-to-end test pass.

Test Plan:
tools/runtests.py bigbingo
tools/runtests.py third_party/tinyquery

Reviewers: colin

Reviewed By: colin

Subscribers: benkraft

Differential Revision: http://phabricator.khanacademy.org/D11689