Fixed path examples to use new pre=defined color static member objects rather than old, eliminated pre-defined color static member functions.

Author: mikebmcl

source/path-examples.tex

@@ -20,8 +20,8 @@
 
 int main() {
   auto imgSfc = make_image_surface(format::argb32, 300, 200);
-  brush backBrush{ rgba_color::black() };
-  brush foreBrush{ rgba_color::white() };
+  brush backBrush{ rgba_color::black };
+  brush foreBrush{ rgba_color::white };
   render_props aliased{ antialias::none };
   path_builder<> pb{};
   imgSfc.paint(backBrush);