Document the code everywhere, and enable missing docs lints

[MOZGIII]

[dmitrylavrenov]

Looks like it's enabled in our code already. And we can close the issue @MOZGIII ?

[MOZGIII]

No, there are still occasional allow(missing_docs) and etc present: https://github.com/search?q=repo%3Ahumanode-network%2Fhumanode%20missing_docs&type=code