Numericalunits

works for older versions but I'm not promising); random initializations now span more orders of
magnitude; update to latest CODATA.

CODATA as of July 2018.

and a few more constants (μ0, ε0, σSB, αFS). (note that unicode identifiers only work in Python 3)

version 1.19, 2017-11-12 -- no code change, just edited README.

so that code completion libraries are more likely to find the unit names.