[notes] opentimestamps.org python client

[Karl]

- opentimestamps.org simply uploads its payload to an op return transaction

- the python client looks nice; it can connect to either a local node
or a remote server

- it has a bunch of political boilerplate around hashing content.
this boilerplate could be removed and it could be used a simple
op_return client to notarise small data for public lookup

the file hashing boilerplate entrypoint is in
opentimestamps-client/otsclient/cmds.py lines 155-182 (off
616718cfdc5c235ea71374d6910235d77ec47fc0 ).  It loops over each file,
hashes, adds a nonce, and merkles the hashes.

The resulting merkle tip could be replaced with any short content
(likely of identical length) to notarise this content.

I am not a cryptographer.  I might propose either the first n/2 bytes
of 2 different modern hashes preceded 1-4 bytes of topic-specific
identifier, a common hash such as sha256, or something that can be
searched for elsewhere, such as a cleartext commit hash, an infohash,
or a url in a content-indexed network.

Scrubbing the blockchain for similar strings could help find existing
uses to join a larger community.