rename new_flow_logic subdirectory to a less ambiguous name

The "new flow logic" name was supposed to indicate that it was a continuation of the old branch by the same name, but it is beginning to become clear that it's not "new" any more and it might lead to confusion with "classic mode" flow logic while that still co-exists.
Explicitly name the subdirectory "pressure logic" to give a better idea of what goes in it, init.lua edited accordingly.

pressure_logic/abm_register.lua

@@ -0,0 +1,27 @@
+-- register new flow logic ABMs
+-- written 2017 by thetaepsilon
+
+local register = {}
+pipeworks.flowlogic.abmregister = register
+
+local flowlogic = pipeworks.flowlogic
+
+-- register node list for the main logic function.
+-- see flowlogic.run() in abms.lua.
+
+local register_flowlogic_abm = function(nodename)
+	if pipeworks.toggles.pressure_logic then
+		minetest.register_abm({
+			label = "pipeworks new_flow_logic run",
+			nodenames = { nodename },
+			interval = 1,
+			chance = 1,
+			action = function(pos, node, active_object_count, active_object_count_wider)
+				flowlogic.run(pos, node)
+			end
+		})
+	else
+		minetest.log("warning", "pipeworks pressure_logic not enabled but register.flowlogic() requested")
+	end
+end
+register.flowlogic = register_flowlogic_abm