update documentation to include Float type

[BigBigDoudou]

Issue#

No-Story

Description:

Update documentation for Number#between and Number#within to be more accurate. Indeed, these methods accept Integer and Float and returns an Integer or a Float, depending on the params type.

I've added examples in the documentation so it will be more obvious for next people who read it that they can use these methods to generate floats.

Examples in the yardoc documentation where Numeric is used as type (@return [Numeric]). It is not fully documented but as I understand, it covers these cases where a method accepts and/or returns Integer or Float.

I've changed the documentation for the #normal method (replacing Integer, Float by Numeric to keep consistency in the documentation).

[koic]

Nice improvement!