Block log

Logging settings:

• path — the path of the log.
• level — logging level.
• background — if true, then the log is duplicated in stdout.

Logging levels:

• 5 — all communications;
• 4 — all communications except DEBUG;
• 3 — not lower than WARNING;
• 2 — not lower than ERROR;
• 1 — CRITICAL only.
• 0 — disables logging.