Implement Chaum Pederson Signature for Keypair

[drskalman]

Implementing Chaum Pederson Signature for fast single BLS signature verification.

[burdges]

A priori, this should be required before merging anything into substrate, as migration could be painful otherwise.

I'd suggest we deprecate this whole crate though and start another one without this swapable traits mess.

[burdges]

We should merge features of this repo into and deprecate this repo for nugget_bls which does this correctly.