Dancing Rook
============
    
Consider a list of :class:`int` where each number represents a shift of position over the list. Let's define a "dance move" from position ``i`` over a list ``L`` as moving to the position ``i+L[i]``. Thus, dacing over a list ``L`` from a given initial position ``i0`` is doing dance moves starting at ``i0``  until it shifts outside the range of ``L`` (being the range the interval of **valid indexes** of a Python list).

Write the following function in the module with the same name (file :file:`dancing_rook.py`):

    .. py:function:: dancing_rook(L, i0)

such that *given*
    
    - ``L``  a list o :class:`int`
    - ``i0`` :class:`int`
    
does two things:

    - **returns**  a list of  :class:`int` with all the positions that it "danced over" (including the initial one)
    - **modifies** ``L`` by assigning a :class:`str` ``'.'`` to all positions traversed by dancing over ``L`` from the initial position ``i0`` until it shifts onto a position whose value has already been changed to '.' or it falls outside the range of ``L``.

Per exemple:

   .. literalinclude:: dancing_rook-test.txt
      :language: python3
      :start-after: --ini
      :end-before: --fi

Doctests are available at the file :download:`dancing_rook-test.txt <dancing_rook-test.txt>`.