thoroughly optimized polyCub.SV code (about 27% faster now):
- use mapply(.polygauss.side, ...) instead of the for-loop in
  previous .polygauss function (now directly in polygauss)
- .polygauss.side returns nodes_x, nodes_y, weights vectors in a list
  (omit cbind)
- use tcrossprod() for nodes calculation in .polygauss.side
- less object copying
tried sublist_extract from Biobase but overall speed-up was not crucial
updated NEWS