Clean up README a bit

- Fix a number of errors ("node install", "Gibber = require('./build/gibber.lib')")
- URL-ify some things
- A little more explanation here and there
- Verify that all examples work as presented
- Add note about `web-audio-api` build on Windows (from experience)
I couldn't get this to work at all, so I expanded the section on running under Node.js