Update structuring.rst

I know that the main page says that these docs are version 4, but i landed on this page, and didn't realise till quite a bit later, that this feature was not present in version 3 of the specification.
Update structuring.rst

Updated to use the wording draft as opposed to version, as version is currently incorrect, as it is still a draft.
Merge pull request #27 from Relequestual/patch-1

Update structuring.rst