RPad coordinate systems

These define typesafe coordinates used by RPad to identify which coordinate system a coordinate is referring to.

The origin (0,0) is in the RPad's bottom left corner for all of them.

Classes
class	ROOT::Experimental::RPadLength::Normal
	A normalized coordinate: 0 in the left, bottom corner, 1 in the top, right corner of the RPad. More...
class	ROOT::Experimental::RPadLength::Pixel
	A pixel coordinate: 0 in the left, bottom corner, 1 in the top, right corner of the RPad. More...
class	ROOT::Experimental::RPadLength::User
	A user coordinate, as defined by the EUserCoordSystem parameter of the RPad. More...