Add CLI command for better LMDB compaction (#193)

* Add CLI command for better LMDB compaction
Docs change for nanocurrency/nano-node#2435
* More --vacuum details

docs/commands/command-line-interface.md

@@ -69,15 +69,20 @@ Clear record history for long term online weight trending
 ### --peer_clear
 Clear cached peers
 
+### --rebuild_database
+Rebuild LMDB database with `--vacuum` for best compaction. Requires approximately `data.ldb size * 2` free space on disk.
+
 ### --snapshot
-Compact database and create snapshot, functions similar to vacuum but does not replace the existing database. Optional `--unchecked_clear`, `--clear_send_ids`, `--online_weight_clear`, `--peer_clear`
-Optional `--confirmation_height_clear` in version 19.0+
+Compact database and create snapshot, functions similar to vacuum but does not replace the existing database. Optional `--unchecked_clear`, `--clear_send_ids`, `--online_weight_clear`, `--peer_clear`.
+Optional `--confirmation_height_clear` in version 19.0+.
 
 ### --unchecked_clear
 Clear unchecked blocks
 
 ### --vacuum
-Compact database. If data_path is missing, the database in data directory is compacted. Optional `--unchecked_clear`, `--clear_send_ids`, `--online_weight_clear`, `--peer_clear`
+Compact database. If data_path is missing, the database in data directory is compacted. Optional `--unchecked_clear`, `--clear_send_ids`, `--online_weight_clear`, `--peer_clear`.
+Optional `--confirmation_height_clear` in version 19.0+.
+Optional `--rebuild_database` in version 21.0+. Requires approximately `data.ldb size * 2` free space on disk.
 
 ### --validate_blocks
 _version 21.0+_ (_version 19.0+_ as `--debug_validate_blocks`)