Support audio streaming

[vinnyoodles]

The gaming experience isn't complete without sound effects. There are a few platforms that can be used as references.

1. The SDL platform supports audio and is written in C.

• The audio data is stored in a buffer of length 1024.
• The sample rate is 44100.
• The setup is called once before the game loop, which seems to do all that is necessary.
• The SDL platform supports audio nicely because it just opens up the audio channel and repeatedly calls the callback when more audio bytes are needed.
• The audio logic seems to run on the same thread, but is asynchronous due to the callback.
• It uses the blip struct to get the audio channel and its data.
• Then, calls memset to store the data into the output buffer.

2. The OpenEmu platform is written in Objective-C.

• Buffer length of 1024, which must be explicitly called.
• The audio data is retrieved at every frame and seems to be stored in a ring buffer.
• The sample rate must be explicitly set and it is 32768 aka 2¹⁵.
• Uses stereo channel (left and right channel).

3. The libretro platform is written in C.

• 1024 sample rate.
• Sets buffer size and sample rate before game loop.
• The audio data is retrieved in callback manner (unsure of what is calling the callback, may be related to the libretro platform)

[vinnyoodles]

The current problem is importing the blip_buf header file which causes compilation errors with the python build.

#include <mgba/core/blip_buf.h>

[vinnyoodles]

Following https://github.com/mgba-emu/mgba/issues/960