`GAP.julia_to_gap` vs. `GAP.Obj`

For users, calling `GAP.Obj` is more natural than calling `GAP.julia_to_gap`, see oscar-system/Oscar.jl/pull/1600. The documentation should express this.
Currently the keyword argument `recursive` is not documented for `GAP.Obj`.

(Should one better call `GAP.GapObj` instead of `GAP.Obj` if one knows that the result is a "non-immediate" GAP object?)