message: Update Breaking Change section with moved misc/fonts/
diff: - 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.
  + - 2018/01/31 (1.60) - moved sample TTF files from extra_fonts/ to misc/fonts/. If you loaded files directly from the imgui repo you may need to update your paths.
  - 2018/01/11 (1.60) - obsoleted IsAnyWindowHovered() in favor of IsWindowHovered(ImGuiHoveredFlags_AnyWindow). Kept redirection function (will obsolete).
  - 2018/01/11 (1.60) - obsoleted IsAnyWindowFocused() in favor of IsWindowFocused(ImGuiFocusedFlags_AnyWindow). Kept redirection function (will obsolete).
  - 2018/01/03 (1.60) - renamed ImGuiSizeConstraintCallback to ImGuiSizeCallback, ImGuiSizeConstraintCallbackData to ImGuiSizeCallbackData.
  