;Task:
Create a directory and any missing parents.

This task is named after the posix <code>[http://www.unix.com/man-page/POSIX/0/mkdir/ mkdir -p]</code> command, and several libraries which implement the same behavior.

Please implement a function of a single path string (for example <code>./path/to/dir</code>) which has the above side-effect.
If the directory already exists, return successfully.
Ideally implementations will work equally well cross-platform (on windows, linux, and OS X).

It's likely that your language implements such a function as part of its standard library. If so, please also show how such a function would be implemented.
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