Fix #414 - add recursive option for mkdir

[humphd]

This fixes issue #414 reworks mkdir to add support for passing {recursive:true} in order to create missing parent paths for a given child directory. I've reworked the existing mkdirp code on the shell to accomplish this. Also included are updates to the docs, and tests.

Our directory creation code doesn't yet take mode into account. I've left a TODO comment in the code, and added support for it at the level of our mkdir function option handling.

[bcheidemann]

@humphd let me know if you want me to finish this for you

[humphd]

@bcheidemann it would be great if you're willing, thank you! I'm slammed with other work.

[bcheidemann]

@humphd no problem, will probably have to wait until next weekend though

[humphd]

Understood. You'll note that I haven't had time to get to it in 2 years, so don't feel any pressure :)

[bcheidemann]

Understood. You'll note that I haven't had time to get to it in 2 years, so don't feel any pressure :)

Thanks! xD