GTK application inspired by dmenu, wimenu, and many others

Also a coding exercise, comparing C, Python and Vala.

All versions work the same:
- they read lines from STDIN and add each line to a GtkListStore.
- these can then be searched/filtered by typing text into a GtkEntry.
- the results can be navigated by Tab or Down to select the next match,
  or Up to select the previous match.
- hit ESC to cancel and close window.
- hit RETURN to print (to STDOUT) either the selected match,
  or whatever is entered in the GtkEntry.

Build C version:
  cd gmenu-c
  gcc -Wall -o gmenu gmenu.c $(pkg-config --cflags --libs gtk+-2.0)

Build Vala version:
  cd gmenu-vala
  valac --pkg gtk+-2.0 gmenu.vala