[Retros] Add units: 13th update - 1NA (27 pieces)

[Mu-Tsun Tsai]

Here's a slight improvement of my earlier 1NA design.
The idea is almost the same, except for the position has one piece fewer,
and the retraction now becomes simpler.

FEN: 1Nb5/nRRppppp/qrp5/kp6/p7/Q1P3P1/PPrPPPP1/K7

Mu-Tsun Tsai