- YOU NOW NEED TO CALL ImGui::CreateContext() AT THE BEGINNING OF YOUR APP, AND CALL ImGui::DestroyContext() AT THE END.
- removed Shutdown() function, as DestroyContext() serve this purpose.
- you may pass a ImFontAtlas* pointer to CreateContext() to share a font atlas between contexts. Otherwhise CreateContext() will create its own font atlas instance.
- removed allocator parameters from CreateContext(), they are now setup with SetAllocatorFunctions(), and shared by all contexts.
- removed the default global context and font atlas instance, which were confusing for users of DLL reloading and users of multiple contexts
(#1565, #586, #992, #1007, #1558)