Putting in scaffolding for mergine the StandingQuery and QueryAccessor classes.

	modified:   libwm/include/standing_query.hpp
Fixing typo in comment.

	modified:   wmserver/thread_connection.hpp
Merge branch 'refactoring' of github.com:OwlPlatform/world-model into refactoring
Adding more explicit instrumentation statements.

	modified:   wmserver/world_model_server.cpp
Checkpoint code; does not compile. StandingQuery class refactoring almost complete.

Some functions (expireURI, etc) need to have static versions for the
solver threads to call or they could call StandingQuery::for_each
and call the individual functions.

	modified:   implementations/sqlite3_world_model.cpp
	modified:   libwm/include/standing_query.hpp
	new file:   libwm/include/threadsafe_set.hpp
	modified:   libwm/include/world_model.hpp
	modified:   libwm/src/standing_query.cpp
More checkpointing. Using the for_each better.

	modified:   implementations/sqlite3_world_model.cpp
	modified:   libwm/include/standing_query.hpp
	modified:   libwm/src/standing_query.cpp
Checkpointing again; compiles but doesn't function properly.

	modified:   implementations/sqlite3_world_model.cpp
	modified:   implementations/sqlite3_world_model.hpp
	modified:   libwm/include/standing_query.hpp
	modified:   libwm/include/threadsafe_set.hpp
	modified:   libwm/include/world_model.hpp
	modified:   libwm/src/standing_query.cpp
	modified:   wmserver/world_model_server.cpp
Code compiles and runs, passes simple tests.

Removed weird r-value stuff in standing queries, they aren't really
required. Some more refactoring may be possible.

	modified:   implementations/sqlite3_world_model.cpp
	modified:   implementations/sqlite3_world_model.hpp
	modified:   libwm/include/standing_query.hpp
	modified:   libwm/include/world_model.hpp
	modified:   libwm/src/standing_query.cpp
	modified:   wmserver/world_model_server.cpp
Adding support for expiration and deletion with new standing queries.

	modified:   implementations/sqlite3_world_model.cpp
	modified:   libwm/include/standing_query.hpp
	modified:   libwm/src/standing_query.cpp
Merge branch 'master' into refactoring