rpn 5.15.6

Improvements for compound unit conversions, e.g.,

c:\>rpn megaparsec barn * cubic_inch convert
0.1882995991 cubic inch

It's still not 100% right, though:

c:\>rpn inch inch pz * * cubic_potrzebie convert
0.0891082093 cubic potrzebie

The correct answer should be 125.94...

c:\sys\ut>rpn inch inch pz * * cubic_potrzebie convert
0.0891082093 cubic potrzebie