Rewrite of delmailuser to enable proper account deletion (again) (#1813)

* rewrite to fix docker-mailserver#1808 (again)
* exiting script correctly now
* over-engineered usage information
the usage is now displayed like a man page and the paging mechanism (i.e. the display of the information) is borrowed from batcat
* fix typos

setup.sh

@@ -127,16 +127,18 @@ SUBCOMMANDS:
 
     ${0} email add <email> [<password>]
     ${0} email update <email> [<password>]
-    ${0} email del <email>
+    ${0} email del [OPTIONS] <email>
     ${0} email restrict <add|del|list> <send|receive> [<email>]
     ${0} email list
 
   alias:
+
     ${0} alias add <email> <recipient>
     ${0} alias del <email> <recipient>
     ${0} alias list
 
   quota:
+
     ${0} quota set <email> [<quota>]
     ${0} quota del <email>
 
@@ -185,7 +187,7 @@ function _docker_image
     fi
 
     ${CRI} run --rm \
-      -v "${CONFIG_PATH}":/tmp/docker-mailserver"${USING_SELINUX}" \
+      -v "${CONFIG_PATH}:/tmp/docker-mailserver${USING_SELINUX}" \
       "${USE_TTY}" "${IMAGE_NAME}" "${@}"
   fi
 }