`proportionmap` input types inconsistent with docs

[JackDunnNZ]

The docs for proportionmap require wv::AbstractVector{<:Real} whereas the method definition has wv::AbstractWeights. It looks like the method will still work if loosened to accept wv::AbstractVector{<:Real} (like countmap) but not sure if this is intentional. Either way, it would be good to align the docs and the method definition