Constants updated by CGPM

[Don Ziems]

The fundamental constants used for measurements have been updated by the 26th General Conference on Weights and Measures.

The previously experimentally measured and uncertain values have now been fixed...to values that don't align with what is currently coded into Speedcrunch.

Page 31 onward of this document describe the changes:

https://www.bipm.org/utils/en/pdf/CGPM/Convocation-2018.pdf#page=31