doc: Add External Project into the top dropdown menu
("CMake-module.html","CMake"), \
("Cuda-module.html","CUDA"), \
("Dlang-module.html","Dlang"), \
+ ("External-Project-module.html","External Project"), \
("Fs-module.html","Filesystem"), \
("Gnome-module.html","GNOME"), \
("Hotdoc-module.html","Hotdoc"), \
