Extension for Unitful

[Kolaru]

It seems like it is mostly possible to use Interval with Untiful:

julia> 1.5u"m" * interval(1, 2)u"m"
[1.49999, 3.0]_com_NG m^2

The only caveat that I found are the set operations that we define for interval only

julia> in_interval(1.5u"m", interval(1, 2)u"m")
ERROR: MethodError: no method matching in_interval(::Quantity{Float64, 𝐋, Unitful.FreeUnits{…}}, ::Quantity{Interval{…}, 𝐋, Unitful.FreeUnits{…}})
[...]

This could easily be fixed with an extension.

(and then IntervalRootFinding should be compatible with Unitful for free, which is cool)