added nk_sdl_handle_grab declarations to demo/sdl_*/ headers

demo/sdl_opengl2/nuklear_sdl_gl2.h

@@ -20,6 +20,7 @@ NK_API void                 nk_sdl_font_stash_end(void);
 NK_API int                  nk_sdl_handle_event(SDL_Event *evt);
 NK_API void                 nk_sdl_render(enum nk_anti_aliasing);
 NK_API void                 nk_sdl_shutdown(void);
+NK_API void                 nk_sdl_handle_grab(void);
 
 #endif
 /*

demo/sdl_opengl3/nuklear_sdl_gl3.h

@@ -24,6 +24,7 @@ NK_API void                 nk_sdl_render(enum nk_anti_aliasing , int max_vertex
 NK_API void                 nk_sdl_shutdown(void);
 NK_API void                 nk_sdl_device_destroy(void);
 NK_API void                 nk_sdl_device_create(void);
+NK_API void                 nk_sdl_handle_grab(void);
 
 #endif
 

demo/sdl_opengles2/nuklear_sdl_gles2.h

@@ -27,6 +27,7 @@ NK_API void                 nk_sdl_render(enum nk_anti_aliasing , int max_vertex
 NK_API void                 nk_sdl_shutdown(void);
 NK_API void                 nk_sdl_device_destroy(void);
 NK_API void                 nk_sdl_device_create(void);
+NK_API void                 nk_sdl_handle_grab(void);
 
 #endif
 

demo/sdl_renderer/nuklear_sdl_renderer.h

@@ -18,6 +18,7 @@ NK_API void                 nk_sdl_font_stash_end(void);
 NK_API int                  nk_sdl_handle_event(SDL_Event *evt);
 NK_API void                 nk_sdl_render(enum nk_anti_aliasing);
 NK_API void                 nk_sdl_shutdown(void);
+NK_API void                 nk_sdl_handle_grab(void);
 
 #if SDL_COMPILEDVERSION < SDL_VERSIONNUM(2, 0, 22)
 /* Metal API does not support cliprects with negative coordinates or large