Fonte:
http://www.dgci.min-financas.pt/NR/rdonlyres/D133879F-DDF0-4AC6-A4BA-797F979BC1CD/0/CIRCTIP2009Madeira.pdf
http://www.dgci.min-financas.pt/NR/rdonlyres/3B02E17D-0F0A-4984-BAEF-196356593E40/0/Circular_3_2009_TabelasRetencaoAcores.pdf
