Effect 0.10

Features:

• Added a code of conduct
• Added two new testing utilities in effect.testing: perform_sequence and parallel_sequence, which make using using and debugging SequenceDispatcher much nicer.
• On Python 3, you can now use the return statement to return values from functions using @do notation.

Bug fixes:

• Fixed a bug where @do would not propagate StopIteration exceptions
• Fixed a bug that prevented @sync_performer-decorated functions from accepting keyword arguments

Other:

• Many documentation improvements