Add an option to load/convert the data as an Array or Dictionary.

Most users transitioning from GAMS are familiar accessing data via arrays. This package should have the ability to convert or load the data directly to an array.

Ideally the array type should have a named index, similar to NamedArrays. The dictionary should be a `DefaultDict` so that indices that do not appear default to zero.

If the package is updated to satisfy the Tables.jl interface then users can load the data into NamedTuples, but this is an immutable structure so the data could not be manipulated.