Add ConstOne and ConstZero implementation

[saona-raimundo]

Solves #104

The implementation requires extra trait bounds on the generic T since the traits ConstOne and ConstZero are not required for the trait Integer.
This is because types that require allocations should not implement ConstOne and ConstZero.
For example, arbitrary precision numbers.

I added the bounds of ConstOne or ConstZero where needed.

[dnsl48]

That looks great, thank you!
Could you please also add a simple test to validate the values of the new traits constants?

[saona-raimundo]

Sure! Done.
Let me know if they are too simple.

[dnsl48]

No, that is good.
Thank you for the contribution!