Fix spelling of _coefficients.
Add constant colum fix in a few other places.

    This is necessary any time a matrix is
standardized.
Add check for non-zero relative penalty.
Add test case for zero rel_penalties.
Add tests for edge cases:
   * zero variance predictors.
   * non non-zero predictors.
Increase data volume for more stable tests.

  Still not sure how to get perfectly stable
tests.  Maybe consider not generating random data
and instead taking data from static files.