Add item numeration from the games

Added the item numeration from the game cartridges to better distinguish them between generations.
Add item generation

Add an automatic way to decide the generation an item comes from.
The items have been numbered the same way in the generations 3, 4, and 5. Generation 2 items need to specify its gen in its item.js specifically.
Add item validation on Pokemon ruleset

Add item validation on Pokemon ruleset to validate non standard items, such as unreleased items in previous gens or mod items.
Merge pull request #211 from Joimer/patch-11

Gens 3 and 4: Fix item checking