setuid for binary removed as default value

The default value for the mode of the beuser binary should not include
the setuid bit (for root, by default). If the module is applied without
any parameters set, it would allow any normal user to change to any other.
Instead, the default is that nobody may switch.
The preferred way of controlling who may call beuser is via sudo.
If needed, setuid can still be enabled by a actively changing the defaults.
Added general information and parameters
Adapted new default $mode in spec-test
Format fix for parameter section
Merge pull request #10 from philippvh/fix/master/suid-removal

Fix/master/suid removal