Support optional origin in $INCLUDE:
$INCLUDE filename origin

Support optional comment in $INCLUDE:
$INCLUDE filename origin comment

Support optional comment in $TTL (RFC 2308):
$TTL number comment

Do not assume "." is origin if origin is not set and sees a @ or
a label without a ".". It should probably fail.  (Don't assume a
mistake means it is a root level label.)

Add verbose option to show what it is adding, not necessarily
in master file format, but in the context of the data source.

Add "check" option to check sanity of master file but don't really
add to data source.

Open questions to document in manual page:

What happens in the database? replaces existing? What if a.foo
existed but new zone file didn't have a.foo, would previous a.foo
in database be removed?