Tables.columntable contract

[bkamins]

The current contract of Tables.columntable is:

Takes any input table source x and returns a NamedTuple of Vectors

However, this contract is not enforced, as AbstractVector other than Vector can be returned.

@quinnj - what is intended (should docstring be fixed or implementation?).

[quinnj]

I think the docstring should be updated. I think it makes sense to just have AbstractVector as the constraint on return type.

[bkamins]

OK - I have opened #325 to discuss this.