[examples] Update audio_raw_stream.c

[dan-hoang]

One of the first examples I played with when I found out about Raylib was audio_raw_stream.c.

I love how easy it is to synthesize stuff in Raylib, but the example did puzzle me for a bit. The big issues:

1. There are two ways to upload data, and both are put in this one example. The reader must sort out what code is necessary to do things the way they want.
2. The mouse controls are unintuitive.

To address (1), I propose to split this example in two: audio_raw_stream.c and audio_raw_stream_callback.c. To address (2), I propose to use the keyboard instead of the mouse.

This commit updates audio_raw_stream.c to

1. Only use the old API (i.e., IsAudioStreamProcessed and UpdateAudioStream). I feel that the old API is more in the spirit of Raylib and so should be the one that takes a plainer name.
2. Use the keyboard instead of the mouse.
3. Remove the use of malloc, free, and memcpy. This is to reduce the number of headers included.
4. Show a more dynamic visualization.

[raysan5]

@dan-hoang thanks for the simplification and @CrackedPixel thanks for the review!