Remove test dir __init__.py

Related: matthewwithanm/pilkit#14
Ignore my Python3 virtualenv
Test that Optimistic strategy doesn't cause reads

Using the Optimistic strategy should prevent IO ops when you cast the
file as a boolean.
Support should_verify_existence on strategies

This prevents extra IO. Different defaults are used for async backends
since we can’t assume that `existence_required` resulted in existence
synchronously.
Test that there isn't IO done when you get a URL