InternedStrings.jl vs ObjectPool

[xiaodaigh]

It might be worthwhile documenting why the ObjectPool approach was used instead of the InternedStrings.jl. A pros and cons write down so that the decisions are remembered.

[tk3369]

See #4 for previous discussions. I wasn't aware of the InternedStrings.jl package. I benchmarked CategoricalArray, PooledArray, and ObjectPool and ended up keeping the ObjectPool implementation. On the other hand, you can easily define a custom array type that holds InternedStrings and pass the respective fill function to SASLib. In the setindex! function, you can make InternedStrings.

[tk3369]

Leaving this issue open for performance benchmarking. Not a priority compared to other issues and I would probably do this after Julia v0.7 is officially released.