Disabled for now; when enabled it will allow faster collection
open and close in the normal case, while continuing to downgrade
when exporting or doing a full sync.
Also, when downgrading is disabled, the journal mode is no longer
changed back to delete.
- tag list stored in a separate DB table
- non-wildcard searches now do full unicode case folding
(eg tag:masse matches 'Maße')
- wildcard matches do simple unicode case folding
- some functions haven't been updated yet, so ascii folding will
continue to be used in some operations
This allows us to add a docstring to .append() so users can see
the names of the arguments that are being passed, and means we
don't have to remember to prepend run_ when calling a hook.
