Clean up documentation.

[jamen]

I would like to rewrite documentation by hand. I don't really like how JSDoc does it.

• [x] Explain audio.js framework versus Audio.
• [x] Rewrite API documentation.
• [x] Rewrite utility documentation for stream API.
• [x] Add flowchart explaining source PCM format (blocks).
• [x] Add demos/examples.
• [x] Update README.