v0.18.0

Fixed

• Fix compilation with glibs2 2.78 and gobj introspection 1.78 (#125).
• Increase reference of transfer full interface parameters (#122).
• Check if object is null before increase its reference (#119).
• Fix array of string properties (#118).

Changed

• Remove hardcoded g_object_ref calls, binding authors now need to implement
  GICrystal.ref/GICrystal.unref for their special types (#123).