New:

• Optimized data storage - only unique users are saved to the storage system. Default users don't take up any space.
• Major API changes/additions - see the JavaDocs for more info (all changes are backwards compatible, but quite a few methods were deprecated)
• Added transient permissions - accessible from the API, this allows developers to add temporary permissions, which are never saved, and expire as soon as the user logs out.
• Huge internal changes to the way permissions are calculated. This may not be noticeable externally, but the code used to calculate permissions and inheritance is much much cleaner now.
• Better support for saving meta/prefix/suffix data for users and groups

Important Changes:

• The "default-group" option has been removed from the config. This was a necessary step to allow for better data storage (see above).

To replicate older setups, simply set default to inherit your old default-group.

Example:
In the last version, you had default-group set to: member

Load the latest version, and run "/luckperms group default setinherit member".