Composition and inheritance: the Julian way

[ChrisRackauckas]

@pdeffebach

First, make sure DataFrames methods only take in AbstractDataFrame . Second, categorize which functions absolutely need to be defined toe AbstractDataFrame to work. Maybe there already exists a list somewhere? Or we could work on getting that list together and shortened. A good start would be to create a new MyDataFrame <: AbstractDataFrame type that is a mirror image of a DataFrame type and seeing how that works.

GitHub - queryverse/IterableTables.jl: Implementations of the TableTraits.jl...

GitHub - JuliaData/DataStreams.jl: [DEPRECATED in favor of...