support dynamic colors for non-dynamic trixls.

don't know if this is very bad for performance, but it might be fun.

js/pixl/public/trixl.html

			for (var pair of trixl.world) {
				var pos = pair[0], data = pair[1];
				var color = data ? (data.color.apply ? data.color(pos, t) : data.color) : trixl.color;
				gl.uniform4fv(program.color, data ? data.color || trixl.color : trixl.color);
				gl.uniform4fv(program.color, color);
				gl.uniformMatrix4fv(program.transform, false, transform(pos));
				gl.drawArrays(gl.TRIANGLES, 0, 6 * 6);
			}