Angle, Radians, Degrees

  Radians: normalize(), to_normalized(), to_degrees(),
           add_in_place(), sub_in_place(), Add, Sub
  Degrees: normalize(), to_normalized(), to_radians(),
           add_in_place(), sub_in_place(), Add, Sub
  Angle: approx_cmp(), approx_eq(),
         interiorize(), to_interior(), scale(), to_scaled(),
         lerp(), Add, Sub