opmem  :  operator members
opfun  :  operator functions
ambig  :  ambiguous calls

  in each:

  Vector2D.h
  Vector2D.cc
  testVector2D.cc  :  a 2D vector with sum and multiplication by a number

  to compile:
  c++ -Wall -o testVector2D testVector2D.cc Vector2D.cc

funct  :  functor
op_io  :  i/o operator functions
