An explanation of the usage and documentation can be found in github:
https://github.com/SebazCRC/GUILib/




Features:

• Lightweight and easy to use GUI creator
• Provides plenty of features to create a custom GUI
• You do not need to listen to InventoryClickEvent anymore
• Supports multi-paged GUIs
• Not tested, but should work on any Minecraft version from 1.8 on
  
• Prevents a few bugs from happening
• You can customize the next / previous page icons

If you like the library and are planning to use it, you can send me a DM to link your plugin here.
You can also leave a review if you want to.

Feel free to use this library in any of your projects