v2.0.0

Version 2 makes a fairly large breaking change.

• The entire groups system has been removed. Deadbolt is supposed to be simple, but groups makes it more complex than it needs to be. If you still need groups, you'll need to implement something yourself. Deadbolt is a permissions library, and that's it.
• A new HasPermissions trait has been added providing a whole new way to work with permissions and users.
• There's no longer a need to call the save() method. Permissions are persistent by default now.
• Minimum PHP version is now 7.3 to match Laravel 7 framework requirement.