New features:
- Scrubbing! Check documentation: [auto_scrub](src/branch/master/docs/config/osd.en.md#auto_scrub)
- Document online-updatable configuration parameters
Bug fixes:
- Fix NaN during PG optimisation if there are nonexisting OSDs in node_placement
- Fix monitor crash on pool deletion
- Clear journal_device and meta_device before initialising the next OSD in automatic mode
- Sync unsynced deletes before overwriting them with a lower version
(reproducted mostly/only after scrubbing)