Fonts: proof of concept support for user textures.

# Conflicts:
#	imgui.h
#	imgui_internal.h

imgui.h

@@ -3905,7 +3905,7 @@ struct ImGuiPlatformIO
 
     // Textures list (the list is updated by calling ImGui::EndFrame or ImGui::Render)
     // The ImGui_ImplXXXX_RenderDrawData() function of each backend generally access this via ImDrawData::Textures which points to this. The array is available here mostly because backends will want to destroy textures on shutdown.
-    ImVector<ImTextureData*>        Textures;           // List of textures used by Dear ImGui (most often 1).
+    ImVector<ImTextureData*>        Textures;           // List of textures used by Dear ImGui (most often 1) + contents of external texture list is automatically appended into this.
 };
 
 // (Optional) Support for IME (Input Method Editor) via the platform_io.Platform_SetImeDataFn() function. Handler is called during EndFrame().