Use jog to as the traversal method in filters

[tarleb]

Use jog instead of walk.

[tarleb]

The function used to traverse a node is now always stored in the _quarto.traverse field. It defaults to walk, but is set to jog for most filters.

[cscheid]

{
  name =...
  traverser = 'pandoc', -- :walk{}
  filter = {
     ...,
     traverse = 'typewise', -- or 'topdown'
  }
}