serialization: included Cacophony::enum_cfg.
System::Context: doc grouping fixes & tidy.¹

1: Oh Doxygen..
Stage: added clone().¹

1: Prelim for context-wide command broadcasting.
Cmd::Status: added fatal and fatal_remote to take terminative behavior.¹

1: These take the behavior of terminating from exceptions (or explicitly)
so that error and error_remote can give userspace an actual distinction
between normal error and completion. Also, most commands should be able
to recover without resorting to GenericTerminate.
System::Context: gave output stages destination, added broadcast().¹

1: This merges the results queue with the output queue.
IO::Datastore::create_object(): throw datastore_object_already_exists with null ID.
Error: added operator<<().
Cmd: added Unit class, changed result flow.

Cmd/Defs:
	renamed ID to IDValue, renamed IDFields to ID;
	reworked ID to use bitwise operations instead of union madness.

Cmd: added Unit class for shared command data and result storage.

Cmd::type_info:
	renamed construct_stage() to make_stage();
	made make_stage() return StageUPtr instead of raw pointer;
	added make() function.

Cmd::StageImpl:
	added template type parameter for command class;
	added execute_typecast() for userspace convenience;
	corrected ensure_traits.

System::Context:
	removed push_local();
	added "done" queue;
	corrected iteration in terminate();¹
	changed all push functions to take non-references.²

Cmd::Node::Create:
	corrected locality errors;
	tied up some loose ends.

Cmd: moved command flow to headers.

1: Gah, was iterating right after an erasure, which would skip the
element following the erased element.

2: Annoying to define a variable when you really don't care to retain
ownership if it fails to push.
System::Context: added localized_error() and localized_fatal().
Cmd::Node::Create: implemented Statement stage; cleaned up command flow; tidy.