extractor: fetch consumables buffs.
Refactored tooltip scanning.

Also get the item name and properly handle single quotes in strings.
Use the database of consumables.
Added an API to do reverse lookup (e.g. buffs for items).
Library database is now upgraded without a pseudo-library.

The database version is created by the extractor.
The reverse lookup is fully rebuilt on upgrade.
Updated luadoc.
README updated.