Implement validate() for GRid numbers
Implement validate() for GRid numbers

holvi/python-stdnum,holvi/python-stdnum,arthurdejong/python-stdnum,t0mk/python-stdnum,arthurdejong/python-stdnum,tonyseek/python-stdnum,arthurdejong/python-stdnum,holvi/python-stdnum,dchoruzy/python-stdnum