QuadraticBezier is incorrect

The equivalent cubic bezier curve to a quadratic bezier has two different control points than the control point to the quadratic.  As such, the length and point function for a quadratic are incorrect.  See [this fiddle](http://jsfiddle.net/flndr/hgttnsu8/6/) for an example from the SVG spec.  The red curve is the original quadratic curves (Q and T).  The blue curve shows the equivalent cubic curve, as is currently implemented.  The yellow curve shows the equivalent cubic curve with the control points [calculated as described here](http://fontforge.github.io/bezier.html). This should fix that issue.

I've also calculated the QuadraticBezier length mathematically, instead of by approximation.