Since Efl.Interpolator's subclasses are used as interpolator class,
Efl.Interpolator class is changed to be an interface.
This change allows Efl.Canvas.Animation to have Efl.Interpolator as its
property in efl_canvas_animation.eo.
Efl.Interpolator class is to interpolate a value.
Efl.Interpolator class has the following interpolation function classes
as its subclasses.
Efl.Interpolator.Linear
Efl.Interpolator.Accelerate
Efl.Interpolator.Decelerate
Efl.Interpolator.Sinusoidal
Efl.Interpolator.Divisor
Efl.Interpolator.Bounce
Efl.Interpolator.Spring
Efl.Interpolator.Cubic_Bezier
Jaehyun Cho
Xavi Artigas
Stefan Schmidt