Add vectorised alignment computation of the traceback

[rrahn]

(preparation for computing traceback in vectorised alignment)

implement two dimensional iterator wrapper that provides the two_dimensional_matrix_iterator but gets an additional parameter in order to select the simd position to give a filtered view over the vectorised traceback matrix that can be used to compute the traceback for one alignment only.

• [x] write test for two dimensional iterator wrapper
• [x] implement two dimensional iterator
• [x] document two dimensional iterator