Add methods to check the properties of a Number

[mpnd]

Having some methods to check the properties of a Number could be useful. For example, isValidLong() to check whether a number can be converted to a valid long or isFiniteDouble to check whether a number can be converted to a finite double.

[Wilko Henecka]

If I understand correctly, you want some methods to test if a Number can be decoded exactly as a Long or Double.
I don't like the suggested names:

• isValidLong() implies that there are invalid Long.
• isFiniteDouble() all Double representations of reals except infinity are finite. Same for Number.

How about: decodesExactlyToLong(), decodesExactlyToDouble(), ...

[mpnd]

Number class has been removed in 84b894a.