Tweak to Radiation Optimization

* Optimized garbage collection of radiation sources until we get qdel() hints.
* Made the RADIATION_LOWER_LIMIT configurable (option for people to save some cpu time)
* Added some comments and broke the proccessor into separate procs for profiling purposes
* Added a changelog.

code/controllers/Processes/radiation.dm

@@ -7,7 +7,12 @@
 	linked = radiation_repository
 
 /datum/controller/process/radiation/doWork()
-	// Step 1 - Sources Decay
+	sources_decay()
+	cache_expires()
+	irradiate_targets()
+
+// Step 1 - Sources Decay
+/datum/controller/process/radiation/proc/sources_decay()
 	var/list/sources = linked.sources
 	for(var/thing in sources)
 		if(deleted(thing))
@@ -20,7 +25,8 @@
 			sources.Remove(S)
 		SCHECK // This scheck probably just wastes resources, but better safe than sorry in this case.
 
-	// Step 2 - Cache Expires
+// Step 2 - Cache Expires
+/datum/controller/process/radiation/proc/cache_expires()
 	var/list/resistance_cache = linked.resistance_cache
 	for(var/thing in resistance_cache)
 		if(deleted(thing))
@@ -32,6 +38,7 @@
 		SCHECK
 
 	// Step 3 - Registered irradiatable things are checked for radiation
+/datum/controller/process/radiation/proc/irradiate_targets()
 	var/list/registered_listeners = living_mob_list // For now just use this. Nothing else is interested anyway.
 	if(length(linked.sources) > 0)
 		for(var/thing in registered_listeners)

code/controllers/configuration.dm

@@ -720,6 +720,9 @@ var/list/gamemode_cache = list()
 					if(values.len > 0)
 						language_prefixes = values
 
+				if("radiation_lower_limit")
+					radiation_lower_limit = text2num(value)
+
 				else
 					log_misc("Unknown setting in configuration: '[name]'")