Improvements to the Curve Javadoc

[richardTingle]

I'm trying to add some javadoc comments to the Curve class (largely because I didn't understand how to use it so have started experimenting with it). Having had a play and a read up on Bézier curves I think this is correct

  /**
   * Adds a control point to the curve. The line will enter the control point with the following
   * rules but may curve between control points so a continuous line is formed.
   *
   * Note that if the implied gradient entering the control point is different from the implied gradient exiting it then
   * the gradient may sharply change (but the line itself will remain continuous).
   *
   * Between each pair of control points acts as an independent cubic Bézier curve defined by the following:
   *
   * anchor 1 - the 'point' of the first control point (the line will pass through this point)
   * intermediate point 1 - the 'out' of the first control point (the line may not go through this point but it controls the initial direction the line exits anchor 1)
   * intermediate point 2 - the 'in' of the second control point (the line may not go through this point but it controls the initial direction the line enters anchor 2)
   * anchor 2 - the 'point' of the second control point (the line will pass through this point)
   *
   * Instinctively you can think of each section "trying" to go from anchor 1 -> intermediate point 1 -> intermediate point 2 -> anchor 2
   * but being smoothed using a quadratic curve such that it may not actually touch the intermediate points.
   * 
   * Note; if this is the first control point the in doesn't matter and if its the last control point the out doesn't matter
   *
   * @param in
   *          the intermediate point immediately before this anchor point.
   *          This is a control point in Bézier curve terminology
   * @param point
   *          the line will pass through this point. This is an anchor point in Bézier curve terminology
   * @param out
   *          the intermediate point immediately after this anchor point.
   *          This is a control point in Bézier curve terminology
   * @return this curve
   */
  public Curve addControlPoint(Vector2f in, Vector2f point, Vector2f out) {

Slightly difficultly I think (according to my reading of Bézier_curves) the addControlPoint method actually adds 2 control points and an anchor, but I can see why the method is like that and I'm not sure I have any better suggestions.

Assuming that's correct I plan to put in a PR to improve the javadoc here as well as put a bit in SizeInfluencer as to how it can be used with a curve to produce a size change over time

[richardTingle]

I now realise, looking more closely at the code, that the X of in and out doesn't actually matter. Is that intentional. I think I can see that the original intention was that it would matter but because the x and t are being treated as the same thing the X of the control points ends up meaningless.

I think I probably could fix that and make it a true Bezier curve (all be it one that requires that the X of each point is equal to or larger that the previous point to avoid any "the line goes backwards in time" nonsense). That change though would mean the curves would change a little for existing users