round all drawn pixl coordinates by default.

you can disable this, but this won't preserve the imprecise pixls upon
redraw. (because we store the pixls in a very crude way.)

js/pixl/public/index.html

		pixl.draw_pixl = function(pos, color, options) {
			var color = color || pixl.color;
			pixl.ctx.fillStyle = color;
			var pos = options.rawValue ? pos : {x: Math.round(pos.x), y: Math.round(pos.y)};
			var screen_pos = pixl.to_screen(pos);
			pixl.ctx.fillRect(screen_pos.x, screen_pos.y, pixl.size, pixl.size);
			pixl.world[pos.x + "," + pos.y] = {color: color};