Provide user support for rc.conf(5) so a user can create a suitable
/etc/rc.conf file to initialise libbsd.
This patch by default adds basic networking support:
cloned_interfaces
ifconfig_'interface'
defaultrouter
hostname
Refer to FreeBSD documentation for examples.
Users can make a single call to have /etc/rc.conf processed, or pass a
file name to a specific configuration file or a text string with line
feeds can be passed to the scripting version of the interface.
The rc.conf support is implemented in terms of directive handlers that
are called based on a regular expression. The design allows new handlers
to be added as needed.
Line concatenation is still to be implemented.
