Lots of changes!
You now can combine 2 books and not only 2 items.

Enchanting cost is now properly calculated. If you want to understand how it's calculated, check this website: Anvil mecanics

Autodect server version to enable/disable the posibility to rename in color. Check this website for the Formatting codes

You can configure the 40 levels maximum (Too expensive) in the config.yml
Big thanks to @Jikoo for letting me use the code from his plugin AnvilUnlocker to achieve this.

You can now configure max level for each enchant.

Some code cleaning...