Remove _dp from integer numerics

- A product of an integer and a double precision gives a
  double precision result. So these integers in formulas
  do not need _dp affixed to them

- A division of an integer by an integer results in integer
  division. If the result is to be a float then one of the
  operands should be double precision.
Merge pull request #7 from has2k1/integers-as-integers

Remove _dp from integer numerics