Allow zone names to be generated parametrically

Allow zone names to be generated parametrically

Special tokens can now be specified in a zone "file" option
in order to generate the filename parametrically. The first
instead of "$name" in the "file" option is replaced with the
zone origin, the first instance of "$type" is replaced with the
zone type (i.e., primary, secondary, etc), and the first instance
of "$view" is replaced with the view name..

This simplifies the creation of zones using initial-file templates.
For example:

   $ rndc addzone <zonename> \
     { type primary; file "$name.db"; initial-file "template.db"