Results marker can be hidden in block attributes (#3706)

```
pandoc -f org -t native
#+begin_src r :exports results :colnames yes
   data.frame(Id = 1:3, Desc = rep("La",3))
#+end_src

#+caption: Lalelu.
#+label: tab
#+RESULTS:
| Id | Desc |
|----+------|
|  1 | La   |
|  2 | La   |
|  3 | La   |
^D
[Div ("tab",[],[])
 [Table ("",[],[]) (Caption Nothing
  [Plain [Str "Lalelu."]])
  [(AlignDefault,ColWidthDefault)
  ,(AlignDefault,ColWidthDefault)]
  (TableHead ("",[],[])
  [Row ("",[],[])
   [Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "Id"]]
   ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
    [Plain [Str "Desc"]]]])
  [(TableBody ("",[],[]) (RowHeadColumns 0)
   []
   [Row ("",[],[])
    [Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
     [Plain [Str "1"]]
    ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
     [Plain [Str "La"]]]
   ,Row ("",[],[])
    [Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
     [Plain [Str "2"]]
    ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
     [Plain [Str "La"]]]
   ,Row ("",[],[])
    [Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
     [Plain [Str "3"]]
    ,Cell ("",[],[]) AlignDefault (RowSpan 1) (ColSpan 1)
     [Plain [Str "La"]]]])]
  (TableFoot ("",[],[])
  [])]]
```

```
pandoc -f org -t native
#+begin_src R :exports none :colnames yes
   data.frame(Id = 1:2, Desc = rep("La",2))
#+end_src

#+caption: Lalelu.
#+label: tab
#+RESULTS:
| Id | Desc |
|----+------|
|  1 | La   |
|  2 | La   |
^D
[]
```
