getAngle = function(p1, p2, props) {
		if(!props) {
			props = ['x', 'y'];
		}
		var x = p2[props[0]] - p1[props[0]];
		var y = p2[props[1]] - p1[props[1]];
		return atan2(y, x) * 180 / Math.PI;
	}
rotation
@param {Object} start
@param {Object} end