Added saveSoundToBlob() to soundRecorder.js - #312

thank you @wahengchang ! This will close https://github.com/processing/p5.js-sound/issues/257

as part of a related issue (https://github.com/processing/p5.js-sound/issues/314) we may want to move these away from the p5.prototype to the SoundFile

@therewasaguy , when can I use the new version included this Pull-Request ?
I need it desperately

@wahengchang you can use it now by compiling p5 sound from source, and it will be included in the next release of p5.js, tho I'd like to move this (and saveSound) to p5.SoundFile / p5.SoundRecorder, before we make it part of the official API. Let me know if you have any thoughts on that, I'm about to take a look!

^ #315 would move saveBlob to SoundFile. I think that's the best home for this method?

I left a comment :)