Add menu externals (#151)

Author: muczc1wek

docs/zengin/scripts/externals/menu.md

@@ -0,0 +1,74 @@
+# Menu functions
+Menu functions are used to perform operations while being in the menu.
+
+!!! Danger
+    The menu functions are only available in the menu parser. 
+
+## Functions
+
+### `Update_ChoiceBox`
+!!! function "`Update_ChoiceBox`"
+    Updates `C_MENU_ITEM` choice box with the current setting.
+    This specific boxes are hardcoded in the function itself:   
+    `MENUITEM_AUDIO_PROVIDER_CHOICE`,
+    `MENUITEM_VID_DEVICE_CHOICE`,
+    `MENUITEM_VID_RESOLUTION_CHOICE`
+    ```dae
+    func void Update_ChoiceBox(var string choicebox) 
+    ```
+
+    **Parameters**  
+
+    - `#!dae var string choicebox` - name of the one of the hardcoded choice boxes
+
+### `PlayVideo`
+!!! function "`PlayVideo`"
+    Plays a video
+    ```dae
+    func int PlayVideo(var string filename) 
+    ```
+
+    **Parameters**  
+
+    - `#!dae var string filename` - name of the video file
+
+    **Return value**  
+    The function returns TRUE if the video was played successfully, FALSE otherwise
+
+### `Apply_Options_Performance`
+!!! function "`Apply_Options_Performance`"
+    Applies the options for the performance, analyzes the system and changes the settings if necessary
+    ```dae
+    func void Apply_Options_Performance() 
+    ```
+
+### `Apply_Options_Video`
+!!! function "`Apply_Options_Video`"
+    Applies the options for the video, changes the resolution and graphics device if necessary
+    ```dae
+    func void Apply_Options_Video() 
+    ```
+
+## Deprecated
+
+### `Apply_Options_Audio`
+!!! function "`Apply_Options_Audio`"
+    Meant to apply the options for the audio, does nothing apart playing an apply sound
+    ```dae
+    func void Apply_Options_Audio() 
+    ```
+
+### `Apply_Options_Game`
+!!! function "`Apply_Options_Game`"
+    Meant to apply the options for the game, does nothing apart playing an apply sound
+    ```dae
+    func void Apply_Options_Game() 
+    ```
+
+### `Apply_Options_Controls`
+!!! function "`Apply_Options_Controls`"
+    Meant to apply the options for the controls, does nothing apart playing an apply sound
+    ```dae
+    func void Apply_Options_Controls() 
+    ```
+