[Feature request] Unitful compatibility

[jakewilliami]

Issue discovered by @AndiMD originally in #295:

Possibly related, Unitful.jl compatibility:

julia> using Polynomials, Unitful
julia> fit([1.0,2.0,3.0,4.0].*u"m", [6.0,4.0,7.0,7.5].*u"m",2)
ERROR: DimensionError ...

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Response from @jverzani on 5th Dec., 2020:

Yeah, [...] I'm not sure there is a proper fix. For fitting, a Vandermonde matrix is constructed with columns which would need units of u^0, u^1, ...,u^n. So currently there is an error as we type that matrix by eltype(x).

Some discussion on the issue of using units with matrices can be found here:
PainterQubits/Unitful.jl#46

with the simplest recommendation being to strip the units and add them back, as needed.

[jverzani]

Thanks @jakewilliami . Hopefully we can close this someday, but at this moment, I'm no so sure how.