Adding audiosynth

Dynamic waveform audio synthesizer, written in Javascript.

Author is Keith Horwood. The source code is currently hosted at
https://github.com/keithwhor/audiosynth , which is where I got this
from.

There was no version number. So I contacted the creator of the library
on Twitter. He said that we could version it at 1.0.0
https://twitter.com/keithwhor/status/471706382379798528
Merge pull request #3301 from JGallardo/master

Adding audiosynth