Implement ff traits on Scalar type

[arthurgreef]

Describe what you want implemented
Implement https://github.com/zkcrypto/ff traits on Scalar type

Describe "Why" this is needed
A clear and concise description of why you need this to be implemented
We would like to use Sonny for circuits in https://github.com/microsoft/Spartan. Spartan requires scalars to implement the ff traits. If we implement the traits in Spartan then we need to create a wrapper type.

Describe alternatives you've considered
Implement Scalar wrapper that implements traits in Spartan.

Additional context
The source on github also seems to be out of sync with the crate with the same version number published to crates.io. Can we get a new release?

Thanks.