types: Are docs on the version specific types ok?

[tcharding]

Currently the types crate uses re-exports so that for a specific Core version the type exists e.g., v18::CreateWallet is a re-export of v17::CreateWallet but v25::CreateWallet is not (because the JSON returned in Core v25 changed).

Note also that while writing the structs in types I used the docs from bitcoin-cli hitting a bitcoind instance for the version in question. This means that the docs on v18::CreateWallet are actually the docs returned by bitcoind v17.

This would not be a problem if the docs didn't change meaningfully between Core versions without a code change as well but I do not know if that is the case.

[GideonBature]

I think docs on version specifics where a method changed significantly is very okay. I feel reflecting that change brings about more clarity.