Initial work at perf improvements for image() with createImage() by caching canvas.
Initial work at perf improvements for image() with createImage() by caching canvas.

jeresig/processing-js,kevinb7/processing-js,guazipi/processing-js,kevinb7/processing-js,jaredly/processing-js,guazipi/processing-js,jaredly/processing-js,jeresig/processing-js,baiyanghese/processing-js,baiyanghese/processing-js