Support for private/reserved/custom TLDs

[carton-of-mice]

URLExtract pulls in the list of TLDs in the root zone, but there are a number of reserved, test or otherwise special use TLDs that are still valid in URLs in at least some contexts.
I'm looking at rfc6761, rfc6762 and rfc7686, for which I think there should be an extract_private property, but a more generic solution like allowing callers to define their own supplementary(or replacement) set of custom TLDs would be sufficient as well.