ABSN playback algorithm illustrations

Forgive if this is double-posting; I'm not quite sure if the github bridge
is working at present to forward commits and pushes.

I've been working on a PR (
https://github.com/WebAudio/web-audio-api/pull/1143) that captures the
proposed ABSN playback algorithm. This PR now sports a number of
descriptive illustrations that should be helpful in understanding how it's
supposed to work. A number of people asked for figures so I wanted to bring
this to the group's attention. I also did my best to annotate the algorithm
with some explanatory language.

You can view the relevant section of the spec here:

https://rawgit.com/WebAudio/web-audio-api/473db2256b2c7005031c803d2a13567079d609de/index.html#playback-AudioBufferSourceNode

I'd love to get final feedback on this as it's one of the larger bits
remaining in the spec, along with the DynamicCompressorNode business.

Cheers,

.            .       .    .  . ...Joe