Longer timeouts in some tests.
Update PyMongo's git hash to the latest.

This is just short of PyMongo's 2.8rc0 release, includes a test fix for the latest
MongoDB 2.8 replica set behavior.
Remove link to example application "Chirp", I no longer maintain it.
MOTOR-48 Add "How to Ask for Help" section to Github readme.
MOTOR-37 Delete tox.ini.

It can't represent the matrix of multiple Tornado versions and other dependencies,
so I'm not willing to maintain it. I'll rely on Jenkins and, to a lesser extent, Travis.
Use motor_test DB in exhaust cursor tests.
Debug test_exhaust_getmore_network_error.
Await replication when clearing a big test collection.

Debug some replication timeouts in later tests.
Skip Twisted resolver test in Tornado < 3.2.2.

Avoid a bug in Tornado's TwistedResolver implementation.
Mention backports.pbkdf2 as optional dependency.
More quickly determine if mongod is running SSL.
Add require_tornado_version utility for tests.
Skip test_max_size in Tornado 3.
MOTOR-58 Demonstrate that pool can exceed max_pool_size.
MOTOR-58 Always enforce max_pool_size.
Skip some GridFSHandler tests vulnerable to GC race conditions.

The combination of Python 3's new garbage collector and old
Tornado versions' tardy file descriptor cleanup means that
some GridFSHandler tests frequently fail in Python 3 and
Tornado 3.