Provide a row-table option?

[nickrobinson251]

Currently data is represented in column-tables (~collection of column vectors), as i expect the most common way to work with the data is with DataFrames.jl; since a DataFrame is a column-table, we can just construct a column-table here rather than constructing a row-table then paying the cost of materialising the columns later.

However, perhaps there's is a use-case for working row-by-row, in which case it could be nice to provide a way to parse the data directly into a row table (~collection/iterable of namedtuples).

Roughly, the current Records are like CSV.File, but we could provide something like CSV.Rows.