- Added the possibility to set Custom Costs based on permissions.
- Implemented 3 types of costs:

• EXPERIENCE: Player's experience points will be used as currency.
• MONEY: In-game currency will be used.
• CUSTOM: Specific items will be used as currency.
  To define the item, use the format CUSTOM:<material>, where <material> is the name of the item(CUSTOM:STONE).

- Implemented PlaceholderAPI placeholders for Actions.
- Updated libraries.
- Added new messages in the configuration file.

It is absolutely necessary to regenerate the configuration file. Before doing so, however, create a backup of the current configuration file. Furthermore, I wanted to inform that it will not be possible to add auto-update for the configuration file.