refs #252

Two configurable options:
- wait for zones to be loaded before starting (default)
- start server and load zones in the background (asynchronous-start on)

mdate-sh cannot be used, because automake won't install it

This adds support for parsing the "-G" flag and opens the dnstap input
file, but does not yet actually generate the dnstap message trace
output.

ref #158

not sure where to put configuration string doc for each module

ref #195

refs #158

- IXFR is no longer experimental
- DNSSEC is no longer experimental, but technical preview

refs #178

Set to 10800s (see reasoning in issue #155).

refs #155

refs #145

refs #145

refs #90