NewFrame() now asserts if neither Render or EndFrame have been called. Exposed EndFrame(). Made it legal to call EndFrame() more than one. (#1423 etc.)

imgui.h

@@ -123,8 +123,9 @@ namespace ImGui
     IMGUI_API ImGuiIO&      GetIO();
     IMGUI_API ImGuiStyle&   GetStyle();
     IMGUI_API ImDrawData*   GetDrawData();                              // same value as passed to your io.RenderDrawListsFn() function. valid after Render() and until the next call to NewFrame()
-    IMGUI_API void          NewFrame();                                 // start a new ImGui frame, you can submit any command from this point until NewFrame()/Render().
-    IMGUI_API void          Render();                                   // ends the ImGui frame, finalize rendering data, then call your io.RenderDrawListsFn() function if set.
+    IMGUI_API void          NewFrame();                                 // start a new ImGui frame, you can submit any command from this point until Render()/EndFrame().
+    IMGUI_API void          Render();                                   // ends the ImGui frame, finalize the draw data, then call your io.RenderDrawListsFn() function if set.
+    IMGUI_API void          EndFrame();                                 // ends the ImGui frame. automatically called by Render(), so most likely don't need to ever call that yourself directly. If you don't need to render you may call EndFrame() but you'll have wasted CPU already. If you don't need to render, better to not create any imgui windows instead!
     IMGUI_API void          Shutdown();
 
     // Demo/Debug/Info