Logging

[nrc]

We do very minimal logging - a total of six locations log any data. Either we should do proper logging, or we should remove those six logging locations and the dependency.

[ekexium]

Some of my thoughts on the slog migration:

• [ ] Pass the logger around and modify all logging macros
• [ ] Make use of the structured logger to propagate txn's info, e.g. start_ts.
• [ ] Choose an appropriate slog format that makes debugging easier.
• [ ] Remove the wrong child!()s
• [ ] Logs for errors, e.g. "drop active txn"
• [ ] Debug logs for trivial opeartions, which is useful in dev/debug
• [ ] Update examples and docs