Xwt TransformPoint(s) proposal

[hwthomas]

I'd like to propose that TransformPoint (ref double x, ref double y ) and TransformPoints ( Point points[] ) are added to the Drawing Context methods, so that a Point (x,y ) or array points[] can be transformed by the Current Transformation Matrix (CTM).

These are probably the most useful methods, although Cairo and GDI also provide TransformDistance, which omits the translation element. As an alternative to the latter, the CTM { get; set; } could be made available, so that more complex transformations like skew could be achieved.

[ermau]

Duplicate of #76