Support for hmac-sha1, hmac-sha224, hmac-sha256, hmac-sha384
and hmac-sha512 has been contributed by Kevin Chen.
+ The tokenizer's tokens are now Token objects instead of (type,
+ value) tuples.
+
Bugs fixed since 1.7.1:
+ Escapes in masterfiles now work correctly. Previously they
+ were only working correctly when the text involved was part of
+ a domain name.
+
When constructing a DDNS update, if the present() method was
used with a single rdata, a zero TTL was not added.