mkdir: Use ArgParser, support creating multiple directories

Author: https://github.com/linusg
Commit: 6fd7966d81
Pull-request: https://github.com/SerenityOS/serenity/pull/1985

Base/usr/share/man/man1/mkdir.md

@@ -1,16 +1,16 @@
 ## Name
 
-mkdir - create a directory
+mkdir - create directories
 
 ## Synopsis
 
 ```**sh
-$ mkdir path
+$ mkdir directories...
 ```
 
 ## Description
 
-Create a new empty directory at the given *path*.
+Create a new empty directory for each of the given *directories*.
 
 ## Examples