Added iterator_proxy classes for exposing container begin()/end().
Log: added report_error() for Beard::Error.
utility: aliased all of <duct/utility.hpp>.
Log::report_error(): scoped error names and removed newline before message.
ConfigNode: reworked node matching; added Flags::collect, iterator proxies, and extra validation info.
Client::Unit: implemented config loading; added more args and config nodes.

Client::Unit:
	added --no-auto opt;
	added "term" config node and terminfo loading;
	made "log" config node optional;
	implemented config loading and validation;
	implemented barebones session creation.
Client/main: log tidy.