Unify documentation under a few common concepts

[udoprog]

This library uses the following concepts:

• Buffer refers to an object holding an audio buffer.
• A sample is a single value from with in a buffer from a single channel.
• Channel refers to a single channel inside of an audio buffer.
• A frame refers to the group of channel at a given offset inside of an audio buffer.

The primary abstraction are buffers that contain 0 or more channels. Each buffer can also be viewed as a sequence of frames, where each frame contains the corresponding sample from every channel in that buffer.