TODO

fix sighash as int vs bin
defp for all unnecessary exports
standardize par / ser syntax

add Message Type prefixes

Tests for messaging symmetry

Tests for everything

figure out how to sort Witnesses for funding tx

standardize use of new_randomness functions so that we can plug in other entropy sources

Do we need to have a contract ID or can Offer ID be enough? 
- what about if an accept is never ack'd and another is? Would this confuse coordinators or offerers? 

Switch order & Contract ID to 32bytes. Store as hex string or bytes? 

write verification into
- Create Offer
    - verify Announcement
- Create Accept
    - verify Announcement
    - verify Offer
- Ack Accept
    - Verify Accept & all signatures
- Finalize Contract (handle Ack)
    - Verify CET Signatures & funding signatures

    DO we need to verify counterparties' scripts? no, as long as they parse to a script, should be good, we dont care if they're unspendable

Test contract_descriptor serialization symmetry