Multiple Configuration Files

Switch to dhcpd.conf.d

This commit adds dhcpd.conf.d as a directory for containing
configuration file fragments.  This permits the dhcpd instance to be
configured almost entirely by the sg-dhcp role, but for additional
assets such as a file containing MAC addresses to be 'dropped in'.  A
script is also provided in /usr/local/sbin/dhcpd-reconf which will
reconfigure the dhcpd server and restart it.

Configuration Refactor

This release parses the multi-network-CARP-capable config format recently developed.

"Simplicity"

This is the last release that is intended for networks where a single gateway is present. All releases beyond this point support CARP and more advanced features.