Add new prefixes

[Eben60]

2022 four prefixes were added. Two for forming multiples: ronna and quetta ("R", "Q") Two forming submultiples: ronto and quecto ("r", "q").

https://www.nist.gov/pml/owm/metric-si-prefixes

[sostock]

Thanks for your contribution!

I think it would be good to add the new prefixes, but there is one aspect to consider: Unitful.rm (rontometre) will collide with Base.rm (function for deleting a file). In principle, this is not a problem (most people will probably use u"rm" instead of importing Unitful.rm), but there is at least a precedent for avoiding these kind of name collisions: the name Unitful.minute was chosen instead of Unitful.min to avoid confusion with Base.min.

Nevertheless, I think we should add these prefixes (they are part of SI after all).

We could consider not exporting the new units from Unitful.DefaultSymbols (this is actually what would happen if we merge this PR as is¹), so that users of Unitful.DefaultSymbols don’t run into this collision ². On the other hand, exporting only some prefixed units and not the others seem inconsistent (and if you just import every symbol from a package you have to expect collisions if that package adds new symbols). Also, Base.rm is probably not as widely used as Base.min.

@giordano What do you think about this?

Footnotes

1. To export the new units from Unitful.DefaultSymbols, the new prefixes would have to be added here as well: https://github.com/PainterQubits/Unitful.jl/blob/bc5dfb2e87b176274c29c4caec1fd79006c16e17/src/pkgdefaults.jl#L698-L699 ↩

2. There are several packages that use Unitful.DefaultSymbols. ↩

[sostock]

The test failures on master are unrelated (they are fixed by #689, which was merged after this PR was posted).

[Eben60]

rm is a commonly used function, and as for rontometer - I'm not sure if any distance having physical meaning can be measured in rontometers.

So personally I'd suggest not exporting the new prefixes from Unitful.DefaultSymbols (any of them - for consistency) and mention that in the documentation.