Improve sort performance

[xiaodaigh]

In DataConvenience.jl I tried out a radixsort based sorting approach and I found there is still some performance gain to be had in the sorting

https://github.com/xiaodaigh/DataConvenience.jl#faster-sorting-for-dataframes

The implementation is quite simple. I just use the sorttwo! function in SortingLab.jl to sort the sorting columns using radixsort and then apply the sorted indices to the rest of the columns.

[nalimilan]

Feel free to make a PR to use radix sort, but first this should be upstreamed to SortingAlgorithms to avoid adding too many dependencies to DataFrames. Does fsort implement things that JuliaCollections/SortingAlgorithms.jl#33 doesn't cover?

[xiaodaigh]

I should really have another go at getting things into SortingAlgorithms.jl.

SortingLab.jl has string sort.

I would say, another approach is to have a Radixsort.jl and clean up the radix sort interface there majorly. Cos we really only need radixsort anyway.

[bkamins]

Great. Thank you for all the work.

I think it is essential to have all the best possible algorithms in SortingAlgorithms.jl and this is a dependency that DataFrames.jl takes.