Add updateItem hook

[jjnich]

This uses the update item hook to delete and recreate the spellcasting entry on the character sheet. I'm sure there's a more graceful way to do this (like reading and updating the spellcasting entry), but this should work.

This solves Issue #9

[jessev14]

Thanks for starting this. Didn't love duplicating the same logic in both hooks, so I just made the entry handling a function that updates an existing entry or creates a new one if an existing entry isn't found.