The problem/use-case that the feature addresses

There is no way today to define a Groups or Roles. Which means that each user access to should defined on its own. 1. No way to easily configure new users by their roles 2. No way to update the ACL rights for a specific group of user without going through all the relevant users.

Description of the feature

ACL SETGROUP <group-name> [on|off] [permissions]
ACL DELGROUP <group>

ACL SETUSER <username> on %<group-name> [other permissions...]

e.g.

ACL SETGROUP readers on +@read
ACL SETUSER user1 on %readers

Override group permissions for a user:

ACL SETUSER user3 on %readers -DEBUG

Remove a user from group

ACL SETUSER user4 on -%readers