Pin down serialized data formats

[garious]

• 4.1 says sha256. Any reason that might change in the near-term?
• 4.1 There's an Index field instead num_hashes
• 4.2 Should num_hashes be the number of hashes-of-sha256-hashes or should it be hashes-of-sha256-hashes + 1, which would include the append() hash. Silk uses the former, which you can see here: https://user-images.githubusercontent.com/55449/36499105-7c8db6a0-16fd-11e8-8b88-c6e0f52d7a50.png. Note how n is 2, not 3.
• 4.5 talks about signing transactions. "ECDSA (or equivalent)" is mentioned in 6.7.3, and the loom implementation uses ed25519. Not sure what the cuda code is up to. It's labeled "ECC".
• 6.2 mentions CBC, but there are alternatives. Does it matter? https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation
• 7.1.2 says ripend in a 160-bit field. Can you call out RIPEMD-160 specifically?
• 7.1.2 looks like that 'unused' box should be on the same row is Last Vote. Great that it says 64 bytes underneath.
• 7.2 No units on bonds and fees.
• Messages in little endian?