Adding wavesurfer.js

Navigable waveform using WebAudio and Canvas.

Source:
[github.com/katspaugh/wavesurfer.js](https://github.com/katspaugh/wavesu
rfer.js)

License: [Creative Commons Attribution 3.0 Unported
License](http://creativecommons.org/licenses/by/3.0/deed.en_US)

Original contributor: [Alex Khokhulin](https://github.com/xoxulin) who
can be contacted at [alex.hohulin@gmail.com](alex.hohulin@gmail.com). I
did not add him as the author because in his own github repo, that is
what is stated in the `package.json`. Perhaps because this seems like
he would have taken more credit if he added his name there. This is
implied by his link to “[the awesome
contributors](https://github.com/katspaugh/wavesurfer.js)!”