Add 3 methods to point class with documented comments.

* `offset`: which offsets the Point object by the specified amount.
* `polar` : which converts a pair of polar coordinates to a Cartesian point coordinate.
* `interpolate` : which determines a point between two specified points.

Author: Jacob Schatz

src/easeljs/geom/Point.js

@@ -99,6 +99,49 @@ this.createjs = this.createjs||{};
 		return this;
 	};
 
+	/** 
+	 * Offsets the Point object by the specified amount. The value of dx is added to the original value of x to create the new x value. The value of dy is added to the original value of y to create the new y value.
+	 * @method offset
+	 * @param {Number} The amount by which to offset the horizontal coordinate, x.
+	 * @param {Number} The amount by which to offset the vertical coordinate, y.
+	 * @return {Point} This instance. Useful for chaining method calls.
+	 * @chainable
+	*/
+	p.offset = function(dx, dy) {
+		this.x += dx;
+		this.y += dy;
+		return this;
+	};
+
+	/** 
+	 * Converts a pair of polar coordinates to a Cartesian point coordinate.
+	 * @method offset
+	 * @param {Number} The length coordinate of the polar pair.
+	 * @param {Number} The angle, in radians, of the polar pair.
+	 * @return {Point} This instance. Useful for chaining method calls.
+	 * @chainable
+	*/
+	p.polar = function(len, angle) {
+		this.x = len * (Math.cos(angle));
+		this.y = len * (Math.sin(angle));
+		return this;
+	};
+
+	/** 
+	 * Determines a point between two specified points. The parameter `f` determines where the new interpolated point is located relative to the two end points specified by parameters `pt1` and `pt2`. The closer the value of the parameter `f` is to 1.0, the closer the interpolated point is to the first point (parameter `pt1`). The closer the value of the parameter `f` is to 0, the closer the interpolated point is to the second point (parameter `pt2`).
+	 * @method offset
+	 * @param {Point} The first point.
+	 * @param {Point} The second point.
+	 * @param {Number} The level of interpolation between the two points. Indicates where the new point will be, along the line between `pt1` and `pt2`. If `f=1`, `pt1` is returned; if `f=0`, `pt2` is returned.
+	 * @return {Point} This instance. Useful for chaining method calls.
+	 * @chainable
+	*/
+	p.interpolate = function(pt1, pt2, f) {
+		this.x = pt2.x + (f * (pt1.x - pt2.x));
+		this.y = pt2.y + (f * (pt1.y - pt2.y));
+		return this;
+	};
+	
 	/**
 	 * Copies all properties from the specified point to this point.
 	 * @method copy