premake: corrected hord-import and config order.
System::Driver: merged datastore and hive maps; emplace rule type when registering.
IO::Datastore: documented implementation-level exceptions.
IO::Datastore: removed erroneous lock check in release_output_stream().
IO::Datastore, Object::Unit: switched to std::is_nothrow_destructible for ensure_traits.
Data::MetaField: corrected construct() return value.
Doc tidy.
doc/Doxyfile: bump to 1.8.5.
doc/Doxyfile: disabled SOURCE_TOOLTIPS.¹

1: We aren't using SOURCE_BROWSER anyways.
System::Driver: added get_rule_type_info(); doc fix.
Rule/Defs: doc tidy.
doc/pages/etc/memory: reformatted.
Added utility header and make_const()¹.

1: Which is apparently not a thing in C++.
IO::PropType: added members docs.
doc: added stub for utility group.
utility: corrected #include for config.hpp.
Implemented rudiments of command system; see full commit log.

Cmd:
	added class Stage to represent a command stage;
	added stub for NodeCreate command.

System:
	added class Context to manage commands;
	implemented command type registration in Driver.