isValidTld UDF. Provided with a list of valid TLDs from IANA, will
return true if the string provided is on the list, false otherwise.
Useful to filter DNS traffic.
Typo fixing for README
Code changes to handle when the tld provided is null, and for
completeness, when the file provided is null as well. Tests updated too.
README with instructions added, as well as data and script for testing