Add CAA record type

src/responses.rs

@@ -481,6 +481,8 @@ pub enum RecordType {
   /// An AAAA record (usually said "quadrupal A") is an IPv6 pointer with a key (domain or subdomain) and
   /// value (IP address).
   AAAA,
+	/// A CAA record is a way to restrict which authorities may create TLS certificates for your domain. Best security practices state that you should set this for any domain you have sufficient control over.
+	CAA,
   /// A CNAME record basically forwards requests from a domain or subdomain to a second domain or
   /// subdomain. It is very common to see this in places where www.example.com and ftp.example.com
   /// use the same server (and IP address) at example.com; now, when switching IP addresses, the address only