fixed --use usage with a = sign
updated documentation for headless mode
fixed exit_status for some situations where it produces wrong values.
updated changelog and buildfiles
updated doc
Merge branch '0.41' into 0.42
added exit hook to cli class
added named parameters to append_if_no_such_line - first part for #143
Merge branch '0.42' of github.com:krimdomu/Rex into 0.42