Introduce common trait which any typenum type implements

[katyo]

In some cases we need type-level numeric parameters which can be both signed and unsigned.
As I see currently corresponding trait is missing in typenum. This would like to be pretty helpful.

I see two ways to implement it:

1. Rename Integer trait to Signed.
   Add new Integer trait which implemented for both Unsigned and Signed. Pros: Clear meaningful trait names. Cons: Breaking API changes.
2. Add new Number trait which implemented for both Unsigned and Signed. Pros: Non-breaking API changes. Cons: Less meaninful trait name.

Can anybody suggest more clear trait name for second solution?

[Qqwy]

The name Integral is used in some contexts as a more general name for "anything integer-like".

As an example, in Haskell, Natural is used for arbitrary-precision unsigned, Integer for arbitrary-precision signed, Word for 32/64-bit unsigned, Int for 32/64-bit signed, and Integral for the trait that they all have in common.