* Display 'RoundButton' shadow in Edit Mode, even it's not accurate, still can get some sense of depth;
 * Add 'RenderScript' part in 'Usage' section in README.md;
 * Improved 'ProxyDrawable' implementation by review 'InsetDrawable' implementation.
 * Change modifier;
 * Fix padding lost problem on 'ViewCompat.setBackground()';
 * Add 'Utils.init()' method to initialize 'Context' and 'DisplayMetrics' object, so functions might not necessary have to pass Context object.
 * Until 'Utils' being initialized with a 'Context' object, it will use 'Resources.getSystem().getDisplayMetrics()' as default metrics, and if that is also missing, then use 'xhdpi' as a guess.
 * Migrate 'Shadow' to 'ShadowDrawable', just like 'RippleDrawable';
 * Fixed several NullPointException bugs;
 * Don't wrap the background if it's already a 'EffectDrawable';
 * Fixed missing call to 'super.onBoundChange()' call bug in 'EffectDrawable';
 * Fixed lost depth of drawable after animation's bug.