Fixed multiple permissions on same role, and with shared root permissions

[janvp]

I had following issue:
Permission A which is a parent permission.
Two children permissions B and C that inherit from A.

I have 2 roles, one that has permission B and one that has permission C.
But I also have a superadmin role that has automatically all the permissions, so it has permission A, B and C. I expected it would have all the permissions of B and C, but in fact it only had the permissions from either B or C, depending which one was inserted last in the database.

I changed the code, so if for example B has permission ['edit' => true] and C has permission ['edit' => false], the superadmin will have permission ['edit' => true], no matter which one of B and C was inserted last in the database.

assumption of the library:
slugs are a list of key-values where the value is always a boolean.

[janvp]

Fixes #196