wrapping Errno::ETIMEDOUT in a Faraday::Error::TimeoutError exception (#322)

Hey guys, thank you for you AWESOME work.

I don't know if the tests are shaped in the best form, if you want this patch, but want it with a different test suite, just let me know and I will try to put it together.

This addresses the issue #322 in respect to wrapping the `Errno::ETIMEDOUT` in a `Faraday::Error::TimeoutError` exception.