Fixes#362 moves vacuum to a dedicated task. This is needed as previous vacuuming on startup on large databases could cause the server to fail to start. By making this a task it avoids this error case, and makes the vacuum more predictable, and only run when required.
Fixes#306 adding command line autocompletion. These are generated to: CARGO_TARGET_DIR/item-hash/out/. These will need to be packaged for distros later, it's unclear how we could use cargo install with these as cargo doesn't support arbitrary artefacts like this (yet?).
