Added easing functions for all-around better animations.

These are Robert Penner's easing functions (http://robertpenner.com/easing/), refactored by CharlotteGore to only take a t parameter (https://github.com/CharlotteGore/functional-easing). Licensed under BSD (the former) and MIT (the latter).

Related changes:
- Added "AnimatedValue" utility class for updating values used in animations.
- MenuButton now uses AnimatedValue to handle its animations (still linear by default).
- Added in-out-back easings on logo, mods, and various other elements; added out-bounce easings on button menu.

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

src/itdelatrisu/opsu/Utils.java

@@ -239,6 +239,22 @@ public class Utils {
 		return val;
 	}
 
+	/**
+	 * Clamps a value between a lower and upper bound.
+	 * @param val the value to clamp
+	 * @param low the lower bound
+	 * @param high the upper bound
+	 * @return the clamped value
+	 * @author fluddokt
+	 */
+	public static int clamp(int val, int low, int high) {
+		if (val < low)
+			return low;
+		if (val > high)
+			return high;
+		return val;
+	}
+
 	/**
 	 * Clamps a value between a lower and upper bound.
 	 * @param val the value to clamp