Fix spelling errors

(cherry picked from commit 19f92dbfa859ca80c096e8c91b55ce91cb3cb296)

_tools/codespell-ignore-lines.txt

@@ -1,2 +1,3 @@
 | ro           | Romanian                           |
 | te           | Telugu                             |
+.. image:: img/expres.png

_tools/codespell-ignore.txt

@@ -4,3 +4,4 @@ lod
 que
 raison
 uint
+subtile

tutorials/performance/optimizing_3d_performance.rst

@@ -59,7 +59,7 @@ offers significant performance increases.
     In some cases, you can adapt your level design to add more occlusion
     opportunities. For example, you can add more walls to prevent the player
     from seeing too far away, which would decrease performance due to the lost
-    opportunies for occlusion culling.
+    opportunities for occlusion culling.
 
 Other occlusion techniques
 ~~~~~~~~~~~~~~~~~~~~~~~~~~