TODO.md

In random order:

• Documentation: Make one

Done:

• ImGui: Factor out changes to ImGui to use vanilla version.
• Editor: Fix variable naming (mainly add m_ prefix)
• Editor: Split NodeEditorImpl.cpp to multiple files, file has grown too big.
• Editor: Factor out use of picojson.h
• Editor: Move use of <optional> to optional code extensions

#57 - join ax::NodeEditor::EditorContext with struct EditorContext and remove reinterpret_cast<>