Up_gtkFontGet
_gtkFontGet retreives the most current settings of a Font object.
Prototype : fun [ObjGtkFont] [S I I I I I I]
- ObjGtkFont : a Font object.
- Return [S I I I I I I] : a tuple with in the order : the name, the size, the style, the variant, the weight, the stretch and the gravity. Or nil if an error occurs (typically an invalid object or not created yet)