Allow ZIP only parsing

[joshco]

Feature request. If the input string is simply a ZIP code, eg "10011", then return successfully with just postal_code populated.
When collecting address information from subscribers, ZIP/postal_code is often considered good enough

[ruckus]

In your own code: if the input string is all digits and 5 characters long - can you just assume its a zip? Seems like overkill to run a 5 digit character string thru this parsing engine if you can essentially "tell" is already a zip.