Adds function to pygame.key module to get key code from name of key

[MyreMylar]

Attempt to add a function to get a key code from a key name. There were some concerns in the original report #309 that this function wouldn't be SDL1 compatible but I'm not sure if that is a huge concern any more.

Also, do I need to add a:

.. versionadded:: 2.0.0 

into the docs?

It's my first first attempt at adding a C extension Function so I may have done some obvious stuff wrong!

[MightyJosip]

Great. Can you also add
def key_code(name: str) -> int: ...
somewhere in the buildconfig/pygame-stubs/key.pyi. And yes it would be a cool addition if you write version in the docs.

[illume]

I think this needs to be more clear in the docs what this is returning.

Mention something about it matching K_* event types and an example like your unit test below?

   Example:

   ::

        >>> pygame.key.key_code("return") == pygame.K_RETURN
        True
        >>> pygame.key.key_code("0") == pygame.K_0
        True
        >>> pygame.key.key_code("space") == pygame.K_SPACE
        True

   .. ## pygame.key.key_code ##

We still want to be able to compile with SDL 1 for pygame 2.

#if IS_SDLv1
/* maybe return 0? How would code that has to work on pygame 1 and 2 work? */
#else  /* IS_SDLv2 */
/*... your code goes here.*/
#endif /* IS_SDLv2 */

The SDL docs for SDL_GetKeyFromName have this note:
https://wiki.libsdl.org/SDL_Keycode
https://wiki.libsdl.org/SDL_GetKeyFromName

Returns key code, or SDLK_UNKNOWN if the name wasn't recognized; call SDL_GetError() for more information.

So your code needs to either raise an error if you get SDLK_UNKNOWN? Or should it just return 0? Maybe raising an error is better.

[MyreMylar]

Added two exceptions:

1. Where the key name is unknown it returns 0 and raises a ValueError.
2. Where pygame is compiled with SDL 1 it should raise a NotImplementedError. Not certain how to test this one, I added a test for it but I don't know if the CI runs that setup.

And I added the example documentation suggested by @illume.

[MightyJosip]

Thanks 👍, I will approve this changes now, but since we are close to the release date I will let illume to decide if we merge it in dev8 or later.

[illume]

🎉 thanks