Add background image for template_toolbelt.p8

* Convert to lowercase template_toolbelt.p8
* Lowercase string to replace in generate_pico8.py

Author: adamscott

generate_pico8.py

@@ -12,5 +12,5 @@
     with open('template_toolbelt.p8', 'r') as r:
         toolbelt_content = r.read()
         r.close()
-    toolbelt_content = re.sub(r'\#INSERT_TOOLBELT\#', lua_content, toolbelt_content)
+    toolbelt_content = re.sub(r'\#insert_toolbelt\#', lua_content, toolbelt_content)
     f.write(toolbelt_content)