Massive "fleshing out" of the project, establishing remaining goals.

• Added FooShadedSteps
• Added AnimatedGradient
  • See also: GradientStoryboard, GradientAnimation, GradientProperty, TweenSpec, & more
• Added GradientCopyWith template
  • Used to override the return type for the Gradient.copyWith method used from within either a GradientTween or AnimatedGradient
• Introduced Gradient getter reversed and convenience method animate()
• Introduced isAgressive flag for GradientTween
• For the generation of MaterialColors via Spectrum.materialColor:
  • Blend -> SwatchMode with an additional value, SwatchMode.complements
  • Consider Spectrum.materialAccent to create a MaterialAccentColor
• Color complements are obtained by new SpectrumUtils.generateComplements
  • Which drives the List<Color> getter extensions on instantiated Colors, too; Color.complementTriad, for example

• Initial release.