Documented preserveDrawingBuffer option

README.md

 - `autoplay` whether playback should start automatically after loading
 - `loop` whether playback is looped
 - `seekable` whether a seek-index is build during load time; neccessary for `seekToFrame` and `seekToTime` methods
+- `progressiveThrottled` whether to throttle downloading chunks until they're needed for playback. Requires `progressive`; default `false`.
 - `onload` a function that's called once, after the .mpg file has been completely loaded
 - `ondecodeframe` a function that's called after every frame that's decoded and rendered to the canvas
 - `onfinished` a function that's called when playback ends

jsmpg.js

 	this.wantsToPlay = this.autoplay;
 	this.loop = !!opts.loop;
 	this.seekable = !!opts.seekable;
-  	this.preserveDrawingBuffer = !!opts.preserveDrawingBuffer;
+  this.preserveDrawingBuffer = !!opts.preserveDrawingBuffer;
 	this.externalLoadCallback = opts.onload || null;
 	this.externalDecodeCallback = opts.ondecodeframe || null;
 	this.externalFinishedCallback = opts.onfinished || null;
 
 	// attempt to get a webgl context
 	try {
-    		var options = { preserveDrawingBuffer: this.preserveDrawingBuffer };
+    var options = { preserveDrawingBuffer: this.preserveDrawingBuffer };
 		gl = this.gl = this.canvas.getContext('webgl', options) || this.canvas.getContext('experimental-webgl', options);
 	} catch (e) {
 		return false;