Ensure destination directory exists

[jmcphers]

Hey, thank you for this very useful script! I hit an error when I first tried to use it because the output man page path didn't exist and Pandoc doesn't automatically create it. This small change ensures that the path will exist when Pandoc tries to write to it.

[ronaldtse]

Thank you @jmcphers ! Very glad to know the module is useful for you and happy to merge! 🙇