Additional radian based methods

Added radian based mothods with Rad suffix.

I additionally created new radian/degree conversion values in MathUtils that match Java naming convention. (ALL_CAPS)

I given them short names like RADIANS and DEGREES instead of something like RAD_TO_DEG. Hopefully this isn't confusing. Anyway javadoc comment is added to clear this up.

If those are fine, the old camelCase ones perhaps should be removed?