G_APPLICATION_DEFAULT_FLAGS is not defined in older version. 0 is defined
everywhere.

G_APPLICATION_FLAGS_NONE is deprecated in newer gtk

I will leave it for another day. can't locate problem now.

when it is not called, default locale is C, which will result in g_message,
g_print etc print garbage (???) on utf-8 string.

add doc on how to compile from source.

force label color to be black on these themes

zero-panel should show in the monitor that emacs runs.
move_window() is updated to support multiple monitor setup.

add notes on meson version requirements.

added more details

so that gtk-im-module project can use the C client.