Improved docs
Various fixes

- updated syntax, removed action:
- allow for a user shell for created user
- change default variables, else one must always customize all variables
- add duraconf settings for ssh, make them optional
check for subelement so that by defining an invalid hardening_user, user creation is skipped
No UsePAM prevents all logins
Merge branch 'improve_docs'
Improve variable names update documentation