FastMath: new utility methods

[capdevon]

New static methods:

• insideUnitCircle(): Returns a random point inside or on a circle with radius 1.0
• insideUnitSphere(): Returns a random point inside or on a sphere with radius 1.0
• onUnitSphere(): Returns a random point on the surface of a sphere with radius 1.0
• nextRandomFloat(float min, float max): Returns a random float within [minInclusive..maxInclusive]

From Unity API:
https://docs.unity3d.com/6000.0/Documentation/ScriptReference/Random.html

these features are incredibly useful and widely used in Unity demos

add Test class