We are so strong with the more general Tables.jl abstraction. Tables.jl took us a step away from having lots of types of `AbstractDataFrame`. Subtyping `Abstrac

We are so strong with the more general Tables.jl abstraction. Tables.jl took us a step away from having lots of types of `AbstractDataFrame`. Subtyping `AbstractDataFrame` is hard, I have to deal with two packages that do it and it is a big and not entirely documented interface. More natural is extending Tables.jl (like DataFrames and JuliaDB does). and we continue to build more tools that are table agnostic, and have APIs that DataFrames and a distributed table package special case when they can do it more efficienctly