Pysdl2-cffi

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- ``sdl.*`` bindings are generated directly instead of using apipkg. Works
better with IDE autocomplete.
- _sdl.lib.SDL_* (non-renamed) wrappers have been removed. The raw cffi
functions are still available in __sdl.lib, __sdl_image.lib etc.
- SDL math and string functions have been removed. Use the Python equivalents.
- __str__ representation of all structs.
>>> print(sdl.Rect((0,0,12,42)))
<Rect x=0 y=0 w=12 h=42>
- Struct properties return and accept wrapper classes instead of raw
cffi objects in many places.
``isinstance(sdl.Surface().clip_rect, sdl.Rect) == True``
Lessens the need to use lower-level cffi functions.
- ``sdl.Event().unwrapEvent()`` added to convert a generic event into the
correct union member e.g. ``WindowEvent``, ``KeyboardEvent``, ...

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- Updated for cffi 1.0. Uses a compiled extension instead of dlopen. Much
faster on CPython.
- Can automatically grab SDL2 dependencies on Windows.

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- Struct wrappers now expose all the attributes of the C-level struct as
properties. Great for tinkering, as the property names can now be
inspected interactively.
- Struct wrappers no longer pass all attribute access through
getattr/setattr. Arbitrary data can be attached to the struct wrappers
as is customary in Python.
- Fix a capitalization error for the "classy" API to conform to the general
binding rules. ``ob.gL_Function`` is now ``ob.GL_Function``.

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- Windows is now supported! You must manually download the SDL2 dll's and
place them on PATH ``set PATH=%PATH%;C:\users\me\SDL2Dir`` but pysdl2-cffi
will attempt to load the Windows ``.dll`` as well as the Unix ``.so``.

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- Enums are no longer wrapped in (nonexistent) classes
- Python 2 can also pass Unicode where char* is required; automatically
encoded to utf-8.