update reference index page to list all sub sections and in the nav order

Author: bosh

docs/reference/index.md

@@ -11,12 +11,14 @@ looking for something specific.
 
 * [Config File Reference](../config/index.md)
 * [Game Variables](../game_vars/index.md)
-* [Player Variables](../player_vars/index.md)
 * [Machine Variables](../machine_vars/index.md)
-* [Config Players](../config_players/index.md)
+* [Player Variables](../player_vars/index.md)
 * [Event Reference](../events/index.md)
+* [Config Players](../config_players/index.md)
 * [Assets](../assets/index.md)
 * [Shows](../shows/index.md)
 * [MPF Errors](../logs/index.md)
 * [Example Games](../examples/index.md)
 * [Code Extensions](../code/index.md)
+* [API Reference](../code/api_reference/index.md)
+* [BCP Protocol Specification](../code/BCP_Protocol/index.md)

mkdocs.yml

@@ -1523,7 +1523,7 @@ nav:
       - code/api_reference/misc_components/DelayManager.md
       - code/api_reference/misc_components/DelayManagerRegistry.md
 
-  - BCP Interface:
+  - BCP Protocol Specification:
     - code/BCP_Protocol/index.md
     - ball_start (BCP Command): code/BCP_Protocol/ball_start.md
     - ball_end (BCP Command): code/BCP_Protocol/ball_end.md