Generalize & improve underlying interfaces

[liamsi]

@evan-forbes made some interesting suggestions to generalize the underlying interface from a merkle tree to a vector commitment prover; see:
#9 (comment)

[liamsi]

Related to this @Wondertan also brought this draft / write-up (?) to my attention: https://math.mit.edu/research/highschool/primes/materials/2018/Kuszmaul.pdf

It analyses bandwidth requirements and shows how to significantly improve on bandwidth while slightly increasing computational complexity. VCs are certainly something we should look into post-launch.