Support iteration of data using both name and column index.

[bausshf]

As written here: #188 (comment)

It was suggested to make an issue of its own about this, which I agree with.

So basically it would be a nice addition to iterate through the column names without multiple calls to retrieve the names.

This will help to simplify implementation, but should also increase performance.

[schveiguy]

I think just in general support for iteration via things like byValue, byName, byNameValue would be nice.