Option to add directory

[willmcgugan]

This is an attempt to resolve #120

I'm looking for early feedback. Happy to make any changes if there is an agreement on the idea, and I can update the docs. BTW this work is sponsored by my client :)

The gist is that there would be a new section in the configuration that would check if a directory exists, and optionally create it. Here's an example:

[directory:foo]
path = /foo/bar
create = True
mode = 777

Only path is required. If create is True, the directory will be created if it doesn't already exist. If create is False (the default), then it will fail if the directory doesn't exist.

Should the directory config have a chown value to set ownership of the new directory?