- trully background parsing now works !
 * added stl-utils.js file that contains utilities (isBinary) etc
which could be used both inside worker and main thread
 * moved pre-processing (isBinary, ensureBinary, ensureASCII) to inside
the web worker in case web workers are used, which means no more blocking of the main UI !

- modified api to return a DEFERRED, not a promise, so that processing
can be cancelled (by rejecting the deferred).
 * only works for web worker variant

- added semi-fake progess notification : progress is set to 100% at end of parsing
 * need to look into ways to reflect actual parsing