doxygen: wrap some game controller code examples in "```c" blocks.

include/SDL_gamecontroller.h

@@ -99,6 +99,8 @@ typedef struct SDL_GameControllerButtonBind
 
 /**
  *  To count the number of game controllers in the system for the following:
+ *
+ *  ```c
  *  int nJoysticks = SDL_NumJoysticks();
  *  int nGameControllers = 0;
  *  for (int i = 0; i < nJoysticks; i++) {
@@ -106,6 +108,7 @@ typedef struct SDL_GameControllerButtonBind
  *          nGameControllers++;
  *      }
  *  }
+ *  ```
  *
  *  Using the SDL_HINT_GAMECONTROLLERCONFIG hint or the SDL_GameControllerAddMapping() you can add support for controllers SDL is unaware of or cause an existing controller to have a different binding. The format is:
  *  guid,name,mappings
@@ -119,8 +122,10 @@ typedef struct SDL_GameControllerButtonBind
  *  Buttons can be used as a controller axis and vice versa.
  *
  *  This string shows an example of a valid mapping for a controller
- *  "03000000341a00003608000000000000,PS3 Controller,a:b1,b:b2,y:b3,x:b0,start:b9,guide:b12,back:b8,dpup:h0.1,dpleft:h0.8,dpdown:h0.4,dpright:h0.2,leftshoulder:b4,rightshoulder:b5,leftstick:b10,rightstick:b11,leftx:a0,lefty:a1,rightx:a2,righty:a3,lefttrigger:b6,righttrigger:b7",
  *
+ * ```c
+ * "03000000341a00003608000000000000,PS3 Controller,a:b1,b:b2,y:b3,x:b0,start:b9,guide:b12,back:b8,dpup:h0.1,dpleft:h0.8,dpdown:h0.4,dpright:h0.2,leftshoulder:b4,rightshoulder:b5,leftstick:b10,rightstick:b11,leftx:a0,lefty:a1,rightx:a2,righty:a3,lefttrigger:b6,righttrigger:b7",
+ * ```
  */
 
 /**
@@ -174,7 +179,7 @@ extern DECLSPEC int SDLCALL SDL_GameControllerAddMappingsFromRW(SDL_RWops * rw,
  *
  * This string shows an example of a valid mapping for a controller:
  *
- * ```
+ * ```c
  * "341a3608000000000000504944564944,Afterglow PS3 Controller,a:b1,b:b2,y:b3,x:b0,start:b9,guide:b12,back:b8,dpup:h0.1,dpleft:h0.8,dpdown:h0.4,dpright:h0.2,leftshoulder:b4,rightshoulder:b5,leftstick:b10,rightstick:b11,leftx:a0,lefty:a1,rightx:a2,righty:a3,lefttrigger:b6,righttrigger:b7"
  * ```
  *