Add on_server_startup event

Add startup event to the Clusterio module API which is raised at startup
of a Factorio server.  This is to server as a replacement for the
on_init and on_configuration_changed events which cannot be used in
modules.

Adds clusterio_patch_number global from the patcher in order to
implement this.  This is a number that's incremented every time the save
is patched.

modules/clusterio/impl.lua

@@ -1,9 +1,17 @@
 local api = require('modules/clusterio/api')
 
-
 local impl = {}
 
-local function init()
+
+impl.events = {}
+impl.events[defines.events.on_tick] = function()
+    if global.clusterio_patch_number ~= clusterio_patch_number then
+        global.clusterio_patch_number = clusterio_patch_number
+        script.raise_event(api.events.on_server_startup, {})
+    end
+end
+
+impl.events[api.events.on_server_startup] = function()
     if not global.clusterio then
         global.clusterio = {
             instance_id = nil,
@@ -15,7 +23,6 @@ end
 -- Internal API
 clusterio_private = {}
 function clusterio_private.update_instance(new_id, new_name)
-    init()
     global.clusterio.instance_id = new_id
     global.clusterio.instance_name = new_name
     script.raise_event(api.events.on_instance_updated, {
@@ -35,14 +42,12 @@ function impl.add_remote_interface()
         -- Returns the instance id the game is run under
         -- This may change over time and/or be nil.
         get_instance_id = function()
-            init()
             return global.clusterio.instance_id
         end,
 
         -- Returns the name of the instance the game runs under.
         -- This may change over time and/or be nil.
         get_instance_name = function()
-            init()
             return global.clusterio.instance_name
         end,
     })