Name columns without outputting a dataframe

[dukebody]

In #73 we added the possibility of outputting a dataframe with named columns to implement #70

However in some cases one would want to get the "columns" names and still get an ndarray as output, for performance reasons.

This shouldn't be hard to do. Names can be stored in a names attribute in the dataframemapper after transform. @dcbb

[dukebody]

Fixed in 2fc6286 (#83). Thanks @ragrawal !