Add Thomson

[spease]

Would be nice to have Thomson and Dalton available as derived units. The definition can be found on this page:
https://en.wikipedia.org/wiki/Thomson_(unit)

Barring that, it'd be helpful if a guide existed on how to derive units yourself.

[paholg]

Sorry, I guess I never noticed this issue. If you're still interested in adding derived units, you can add them to the derived! call in the appropriate unit system in src/build.

For example, you can see the Newton defined here:

dimensioned/src/build/si.rs

Line 24 in 3ef45da

N: Newton = Kilogram * Meter / Second2, Force;

The format is CONSTANT_NAME: TypeName = *EXPRESSION*, Dimension;

The trailing , Dimension part is optional, but if included, should be a trait located in this file: https://github.com/paholg/dimensioned/blob/3ef45da755694ed56ed6e7d6c3114f19fd1f29d0/src/dimensions.rs