RUBY-2807 - Compression warning (proof-of-concept)

[johnnyshields]

This PR adds a simple warning log message if compression is not enabled. It also adds an option warn_compression_disabled which can be set to false to silence the message.

This warning message would go a long way to help users avoid mistakenly not setting compression. (Note that this PR does not enable any compression by default.)

I am not that familiar with the best to implement this in driver, so if the team agrees with this POC it would be great if someone could take it to the finish line.