Expose compute_kzg_proof

[jtraglia]

This exposes the compute_kzg_proof in the way described here:

• EIP4844: compute_kzg_proof() now takes bytes as input consensus-specs#3219 (review)

This PR will:

• Replace BLSFieldElement with Bytes32 in many places.
  • These are not guaranteed to be valid field elements and what I did before was misleading. Sorry.
• Add compute_kzg_proof to the readme.
  • Also sort the entries in a more logical order.
• Create compute_kzg_proof_impl and move bulk of work there.
  • This allows us to pass a polynomial to it from compute_aggregate_kzg_proof.
• Use f->bytes for calls to bytes_to_g1 & bytes_to_bls_field.
  • This is a lot cleaner in my opinion.

Fixes #34.

[jtraglia]

So I just learned that I changed some things I shouldn't have and it no longer matches the spec. Let me fix those things and then it will be ready for review. Sorry.

[asn-d6]

Let's not merge this just yet. Actively workign on it.

[jtraglia]

Okay I think this is ready now. Please review.