Implement Chained Transform

[glennmoy]

It might be convenient to enable multiple Transforms to be applied in a Chain (cf https://invenia.github.io/Impute.jl/stable/api/chain/).

However there are a number of caveats/challenges to this that we would first have to address:

1. There is no way to propagate the required kwargs for each component transform unless they were part of the constructor. (this is the most limiting aspect).
2. The chain would only be mutating iff all the component transforms were mutating.
3. Unless all component transforms are mutating, successive transforms could only be applied to the result of the previous one. e.g. if we applied one transform to some subset of the data (say combining cols :a and :b) that is non-mutating then we would be restricted to working with just that result from there on. We could not use it with the parent data anymore.

#38 applies to points (2) and (3).

There are probably numerous other issues I'm not thinking of right now.