Clean up imports
Add more tests

A fix needed to be made in greenio.py which as revealed by the test. Globals
have been renamed for the fix.
Fix test by setting timeout after connecting

This tests for recv() timeout, so it onlt makes sense to set the timeout after
connecting, just before calling recv().
Clean up module-level attributes

Module-level attributes have been renmaed to avoid confusion and improve code
clarity.
Add python version guard
Add test for send timeout