Add whisk dev-friendly API

[dapplion]

WIP: Ease integrating underlying crypto into clients that follow spec defined in ethereum/consensus-specs#3205

• is_valid_whisk_shuffle_proof
• generate_whisk_shuffle_proof
• is_valid_whisk_tracker_proof
• generate_whisk_tracker_proof

[asn-d6]

OK this is a more interesting PR :-)

Please let me know when it's ready and I will review.

[dapplion]

Yeah this branch is what I'm using in the lighthouse PoC, and so far so good

[asn-d6]

Thanks for this! There are a few things that could be improved in terms of code quality and docs but let's get this merged to move on with development and we can do a round of cleanups later down the road.