Declaration of new functions
Merge branch 'master' of https://github.com/jeremyletang/rgtk
New widgets: Dialog and AboutDialog
Merge branch 'master' of https://github.com/jeremyletang/rgtk

Conflicts:
	gtk_glue/gtk_glue.c
	src/gtk/ffi.rs
	src/utils/cast.rs
New widgets : Dialog and AboutDialog