Make sorting optional

[wvengen]

Ancestry does not do sorting by default, and this gem currently requires the presence of a sorting attribute.
Could the sorting become optional (e.g. by setting sorting_attribute to nil)? Then only the hierarchy would be updated but not the pos attribute (or whetever is configured).

[maxivak]

Updated in v. 0.0.9.
see the doc

• Example. For model with ancestry.
  If you use ancestry in model - set :parent_method to 'parent'.

  include SortableTreeController::Sort
  sortable_tree 'ClassName', {parent_method: 'parent', sorting_attribute: 'pos'}

• Example. Do only sorting, without tree.

  include SortableTreeController::Sort
  sortable_tree 'ClassName', {sorting_attribute: 'pos', parent_method: nil}

• Example. No sorting, update only parent.

  include SortableTreeController::Sort
  sortable_tree 'ClassName', {sorting_attribute: nil, parent_method: 'parent'}