Interim commit. Have to think about the "creating user types" issue.
Moved generic storage protocol to sukkiri-db.
Moving type conversion functions into DB module.
Basic DB API mostly complete (?).
Moved DB index code into DB module.
Created new prop-spec code.
Moved db-result->bool into DB module.
Rest of 'moved db-result->bool'.
Got the proptype interface worked out, maybe.