TODO: Add a wish list item

The client should support talking to multiple servers.
etc/nsca-ng.cfg: Add a default "authorize" section

Add an "authorize" section which lets the server start out of the box (instead
of bailing out because the user didn't specify an "authorize" section).  The
new configuration still doesn't permit clients to submit anything to Nagios (it
just allows authenticated clients to talk to the server), so the client will
spit out a "not authorized" message until the user edits the nsca-ng.cfg(5)
file.
etc/nsca-ng.cfg: Give better examples

Improve the clarity of the authorization section examples a bit.
configure.ac: Set AC_CONFIG_MACRO_DIR()

The Autoconf manual suggests to specify the AC_CONFIG_MACRO_DIR(), as it
might be used "by future versions of commands like autoreconf that trace
macro calls".