compat.h: compatibility layer for various GTK versions
util_*: generic, non-UI related utilities
ui_*: ui logic related, but gtk-free utilities
wt_*: custom widgets, cell renderers for gtk - must work in both gtk2 and gtk3
dlg_*: dialog boxes, preferably one per file
bu_*: builders, building a part of a bigger gui portion
in_*: input handling (gtk-specific)

Any of these may depend on glib.
