Add user and permission system

Add users, roles and permissions and rework the authentication to use
separate user and slave tokens for control and slave connections
respectively.

Add commands for listing permissions, roles and users, and creating,
editing and deleting roles and users.

docs/how-it-works.md

@@ -13,3 +13,14 @@ it.  Mods on the other hand work without modifications.
 with a patcher called Hotpatch, but due to the difficulty in supporting
 run time patching and the lack of documentation it was replace it with
 save patching instead.</sub>
+
+
+User Accounts
+-------------
+
+The master server creates and stores accounts for all Factorio users
+that log into instances under its control.  These accounts are used to
+store per player data and authorize management of the cluster.  By
+default users accounts are assigned a Player role that gives a limited
+read access to the cluster resources, and admins of the cluster can be
+assigned an Admin role to get access to manage it.