* documentation and script updates trying to fix#1647
* preparations for refactoring target/bin/
* complete refactor for target/bin/
* changing script output slightly
* outsourcing functions in `bin-helper.sh`
* re-wrote linting to allow for proper shellcheck -x execution
* show explanation for shellcheck ignore
* adding some more information
* Add some checks for user name matching in mail user scripts
* Fix user matching problems in mail user scripts
** fix matching problems at several places:
"delmailuser a@example.com" deletes also user "aa@example.com"
"delmailuser a@sub.example.com" deletes also user "a@sub-example.com"
** similar problems when inserting
** refactor and clean up
This commit adds a script nammed 'listmailuser'. './setup.sh' uses this
this script for its subcommand './setup.sh email list'. A test have
been added too.
