Implement SSshuttles subsystem

* Replaces the shuttle_controller and shuttle process with the shuttles subsystem.  Instead of docking ports being initialized by the game ticker, its part of the StonedMC Master init order.
* The main advantage of this is control over the initialization order, as well as letting Master be aware of CPU we're using up with shuttle processing.
* By being part of the Master init order, we reduce the uncertainty about "are objects initialized yet?" which is nice, since shuttle docks break if machines aren't finished initializing!

code/controllers/Processes/Shuttle.dm

@@ -1,9 +0,0 @@
-/datum/controller/process/Shuttle/setup()
-	name = "shuttle controller"
-	schedule_interval = 20 // every 2 seconds
-
-	if(!shuttle_controller)
-		shuttle_controller = new
-
-/datum/controller/process/Shuttle/doWork()
-	shuttle_controller.process()

code/controllers/shuttle_controller.dm

@@ -1,39 +0,0 @@
-
-var/global/datum/shuttle_controller/shuttle_controller
-
-
-/datum/shuttle_controller
-	var/list/shuttles	//maps shuttle tags to shuttle datums, so that they can be looked up.
-	var/list/process_shuttles	//simple list of shuttles, for processing
-
-/datum/shuttle_controller/proc/process()
-	//process ferry shuttles
-	for (var/datum/shuttle/shuttle in process_shuttles)
-		if(istype(shuttle, /datum/shuttle/ferry))
-			var/datum/shuttle/ferry/F = shuttle
-			if(F.process_state || F.always_process)
-				F.process()
-		else
-			shuttle.process()
-
-
-//This is called by gameticker after all the machines and radio frequencies have been properly initialized
-/datum/shuttle_controller/proc/setup_shuttle_docks()
-//	for(var/shuttle_tag in shuttles)
-//		var/datum/shuttle/shuttle = shuttles[shuttle_tag]
-	for(var/shuttle_type in subtypesof(/datum/shuttle))
-		var/datum/shuttle/shuttle = shuttle_type
-		if(initial(shuttle.category) == shuttle_type)
-			continue
-		shuttle = new shuttle()
-		shuttle.init_docking_controllers()
-		shuttle.dock() //makes all shuttles docked to something at round start go into the docked state
-
-	for(var/obj/machinery/embedded_controller/C in machines)
-		if(istype(C.program, /datum/computer/file/embedded_program/docking))
-			C.program.tag = null //clear the tags, 'cause we don't need 'em anymore
-
-/datum/shuttle_controller/New()
-	shuttles = list()
-	process_shuttles = list()
-

code/controllers/subsystems/shuttles.dm

@@ -0,0 +1,68 @@
+//
+// SSshuttles subsystem - Handles initialization and processing of shuttles.
+//
+
+// This global variable exists for legacy support so we don't have to rename every shuttle_controller to SSshuttles yet.
+var/global/datum/controller/subsystem/shuttles/shuttle_controller
+
+SUBSYSTEM_DEF(shuttles)
+	name = "Shuttles"
+	wait = 2 SECONDS
+	priority = 5
+	init_order = INIT_ORDER_SHUTTLES
+	flags = SS_KEEP_TIMING|SS_NO_TICK_CHECK
+	runlevels = RUNLEVEL_GAME|RUNLEVEL_POSTGAME
+
+	var/list/shuttles = list()	// Maps shuttle tags to shuttle datums, so that they can be looked up.
+	var/list/process_shuttles = list()	// Simple list of shuttles, for processing
+	var/list/current_run = list() // Shuttles remaining to process this fire() tick
+
+/datum/controller/subsystem/shuttles/Initialize(timeofday)
+	global.shuttle_controller = src
+	setup_shuttle_docks()
+	return ..()
+
+/datum/controller/subsystem/shuttles/fire(resumed = 0)
+	do_process_shuttles(resumed)
+
+/datum/controller/subsystem/shuttles/stat_entry()
+	var/msg = list()
+	msg += "AS:[shuttles.len]|"
+	msg += "PS:[process_shuttles.len]|"
+	..(jointext(msg, null))
+
+/datum/controller/subsystem/shuttles/proc/do_process_shuttles(resumed = 0)
+	if (!resumed)
+		src.current_run = process_shuttles.Copy()
+
+	var/list/current_run = src.current_run // Cache for sanic speed
+	while(current_run.len)
+		var/datum/shuttle/S = current_run[current_run.len]
+		current_run.len--
+		if(istype(S) && !QDELETED(S))
+			if(istype(S, /datum/shuttle/ferry)) // Ferry shuttles get special treatment
+				var/datum/shuttle/ferry/F = S
+				if(F.process_state || F.always_process)
+					F.process()
+			else
+				S.process()
+		else
+			process_shuttles -= S
+		if(MC_TICK_CHECK)
+			return
+
+// This should be called after all the machines and radio frequencies have been properly initialized
+/datum/controller/subsystem/shuttles/proc/setup_shuttle_docks()
+	// Find all declared shuttle datums and initailize them.
+	for(var/shuttle_type in subtypesof(/datum/shuttle))
+		var/datum/shuttle/shuttle = shuttle_type
+		if(initial(shuttle.category) == shuttle_type)
+			continue
+		shuttle = new shuttle()
+		shuttle.init_docking_controllers()
+		shuttle.dock() //makes all shuttles docked to something at round start go into the docked state
+		CHECK_TICK
+
+	for(var/obj/machinery/embedded_controller/C in machines)
+		if(istype(C.program, /datum/computer/file/embedded_program/docking))
+			C.program.tag = null //clear the tags, 'cause we don't need 'em anymore