Reimplement (some) ldns sub commands

[mozzieongit]

Initial commands to support:

• key2ds (Key2ds #2)
• nsec3-hash (Implement nsec3-hash #1, Add nsec3-hash command. #6)
• keygen (Add keygen command. #9)
• notify (Notify #7)
• signzone (Add signzone command. #8)
  • basic functionality mostly works but lacks support for most command line arguments.
• dnsupdate (Implement ldns-update and dnst update #10)

Futher commands to support:

• dane
• verifyzone
• walk
• compare zones #102
• readzone
• testns