Added 15 puzzle to side menu.

Fixed typo in collection factory md.

docs/en/en.json

@@ -9,6 +9,10 @@
                         "path": "/tutorials/war-battles",
                         "name": "War battles"
                     },
+                    {
+                        "path": "/tutorials/15-puzzle",
+                        "name": "15 puzzle"
+                    },
                     {
                         "path": "/tutorials/side-scroller",
                         "name": "Side scroller"

docs/en/manuals/collection-factory.md

@@ -45,7 +45,7 @@ Observe that the parent-child relationships between "astronaut" and "probe" are
 
 ## Properties
 
-When spawning a collection, we can pass property parameters to each game object by constructing a table with pairs of collection-local object id:s and tables of script properties to set:
+When spawning a collection, we can pass property parameters to each game object by constructing a table with pairs of collection-local object ids and tables of script properties to set:
 
 ```lua
 -- planet.script