Declare test vector types, maybe aggregate?

[bifurcation]

Right now, test vector processing has to be told what type of test vector it is consuming. We should consider adding a field in a test vector that declares what type of test vector it is. Say something like "type": "tree_math".

It might also be worth producing a unified test vector file format, that pulls together multiple individual test vectors of various types:

{
  "tree_math": { ... },
  "crypto_basics": { ... },
  // ...
}