Creates a directory.
MKDIR [drive:]path
MD [drive:]path
If Command Extensions are enabled MKDIR changes as follows:
MKDIR creates any intermediate directories in the path, if needed.
For example, assume \a does not exist then:
    mkdir \a\b\c\d
is the same as:
    mkdir \a
    chdir \a
    mkdir b
    chdir b
    mkdir c
    chdir c
    mkdir d
which is what you would have to type if extensions were disabled.