Added options menu and menu transitions.

src/utils/asstmngr.lua

@@ -65,14 +65,18 @@ end
 
 function AssetManager:update(owner)
     if self.assets[owner] ~= nil then
-        if self.co == nil then
-            self.co = coroutine.create(_load)
+        if self.assets[owner].co == nil then
+            self.assets[owner].co = coroutine.create(_load)
         end
 
-        local errorfree, retval = coroutine.resume(self.co, self, owner)
+        local errorfree, retval = coroutine.resume(self.assets[owner].co, self, owner)
 
         if errorfree then
             self.assets[owner].done = retval
+
+            if retval then
+                self.assets[owner].co   = nil
+            end
         else
             error(retval)
         end
@@ -96,6 +100,7 @@ function AssetManager:register(owner, asset)
     if self.assets[owner] == nil then
         self.assets[owner] = {
             done = false,
+            co   = nil,
         }
     end