Effect

Incompatible changes:
- Python 2.6 is no longer officially supported, though it might still work for now.

Features:
- Some test utilities have been added to [effect.testing](http://effect.readthedocs.io/en/0.11.0/api/effect.testing.html):
- [const](http://effect.readthedocs.io/en/0.11.0/api/effect.testing.htmleffect.testing.const)
- [conste](http://effect.readthedocs.io/en/0.11.0/api/effect.testing.htmleffect.testing.conste)
- [intent_func](http://effect.readthedocs.io/en/0.11.0/api/effect.testing.htmleffect.testing.intent_func)
- [nested_sequence](http://effect.readthedocs.io/en/0.11.0/api/effect.testing.htmleffect.testing.nested_sequence)

Thanks to manishtomar who contributed the work for this release.

Features:
- Added effect.io, which gives intents for representing print and raw_input-style interactions
- The Func intent now accepts _args and *_kwargs to pass through to the function, and which are compared on `__eq__`, to make testing easier.
- `effect.raise_` is a convenience function to raise an exception instance.
- `effect.testing.noop` is `lambda i: None`, and is intended to be used in `perform_sequence` sequences.
- `effect.perform_delay_with_sleep` is a new performer that performs `Delay` intents by sleeping.
- The exceptions raised from `perform_sequence` have more informative output.

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