PowerDNS - Ensure SPF records are quoted correctly

PowerDNS requires SPF records to be quoted, unlike TXT records which
do not require the quotes.

Change-Id: I3aede09462fdf98dd9dd235e87127afb326f8711
Add more API documentation for record types

Add examples to the REST API documentation section for each of
the record types supported. Currently, there are only examples
for types 'A' and 'MX'.

Change-Id: Iba9a8e4b88312b6266b46fb3e353076dd03cab8f
Fixes: bug #1204578
Merge "PowerDNS - Ensure SPF records are quoted correctly"