Make asciidoc command non-export

Asciidoc is only used by target bob.info and not a user-available
command. I.e. it is entierly an internal command and can be hidden away.
Clean up rpm/package targets

Removes last have-feature variable when the tar-command variable can be used
directly to check if tar is available. Better encapsulation of package and
rpm-target to avoid parsing extra stuff not currently needed.