Add & remove functions for attributes

[MrSorcus]

No description provided.

[kostya]

looks ok, thanks, i not sure about edit attribute, how it should work. maybe as remove-add?

[MrSorcus]

I think - yes.
But what about attribute_remove & attribute_delete?
Just add code like this?

  def attribute_remove(attr : MyhtmlTreeAttrT)
    Lib.attribute_remove(@node, attr)
  end

  def attribute_delete(attr : MyhtmlTreeAttrT)
    Lib.attribute_delete(@tree, @node, attr)
  end

[kostya]

i not think this functions needed right now, because there is no MyhtmlTreeAttrT reference anyway (stored somewhere).