don't use doseq while blitting

goya.canvasdrawing/draw-image-to-canvas is an inner loop. doseq over a
range is a big performance hit, instead use dotimes which compiles down to
a JavaScript primitive loop.
Merge pull request #5 from swannodette/master

don't use doseq while blitting

goya.canvasdrawing/draw-image-to-canvas is an inner loop. doseq over a
range is a big performance hit, instead use dotimes which compiles down to
a JavaScript primitive loop.