The copyright notices listed “Block Notary Inc” as a copyright owner,
which is wrong. The correct owner is POA Networks, Ltd.
Also, add some doc comments to ffi.rs.
This fixes a bug in multiplication that caused a crash (assertion
failure) when the number of iterations was ≥ 130. The code can now
verify its own proofs for t ≤ 128, and matches the reference
implementation for t ≤ ~500.