Added configurable admin role check per ecu-13, as follows:
* Users can edit their own records
* Admins can add, edit, and delete user records
Prevent non-admins from escalating their own permissions by changing their role information.
If a user updates their own record, their session information needs to be updated.
Only admins can delete users.
If an admin deletes their own account, we delete their session and log them out.
Fixed problem with empty user object returned by PUT.
Updated documentation to include details about the new "adminRoles" option.
Merge pull request #15 from the-t-in-rtf/ecu-13

Add checks for admin roles per ecu-13...