Correct a typo in the description of the parameter "rho". This parameter is
relative resistivity and not relative conductivity as previously indicated in the table.
In addition, add some information about wcalc as that
is the replacement for this calculator.
Correct a minor bug involving the metal thickness corrections. Keff and
Z0 will be slightly (usually < 1%) different than with previous versions.
Many thanks to Eric Davis for noting the problem.