DNSDB API Client

 This is a pure C99 program that accesses passive DNS database systems such as:
 .
        * the DNSDB API server at Farsight Security
        * the CIRCL pDNS server at Computer Incident Response Center (LU)
 .
 An API key is required for operation. The command syntax was inspired by a
 Python script called dnsdb_query, but significant departure has occurred,
 largely inspired by a modern understanding of "time fencing" and a desire for
 new features such as CSV output and JSON reprocessing.