Add support for CAA and TXT records

[castillar]

Love the program--nice and simple! I added two command-line flags to look for CAA records (used to control SSL certificate issuance) and for generic TXT records (often used to do domain-level validation for SSL, SAML, etc.).

[jk]

It's not too far fetched, that this tool once will support CNAME records. Therefor -c for the CAA records might conflict then, doesn't it?

[castillar]

Potentially. Since -4 and -6 are being used for A records, we could use -a for CAA records instead, although that might also create confusion. Alternately, CAA is an RR type 257 record, so perhaps -2?

[castillar]

Updated this to use -2 for CAA support, and then added CNAME support as well with -c. :)