Snug

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- python 2 compatibility
- implement overridable ``__execute__``, ``__execute_async__``
- improvements to ``aiohttp``, ``urllib`` clients

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- fixes for sending requests with default clients
- improvements to docs

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- improvements to docs
- fix for ``send_async``

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- improvements to docs
- added slack API example
- ``related`` decorator replaces ``Relation`` query class
- bugfixes

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- improvements to docs
- rename Request/Response data->content
- ``Relation`` query class

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- removed generator utils and serialization logic (now seperate libraries)
- improvements to docs