Performance: please support parsing to Vector[String] rather than List[String]

[benhutchison]

When accessing a collections by numeric index, Vector has much better performance than List, effective constant time vs linear for List [http://docs.scala-lang.org/overviews/collections/performance-characteristics.html]. Indexed access is very common for CSV data.

It is unfortunate that CSVParser currently uses a Vector internally, but then converts to a less-optimal List before returning to client.

It would be easy to support parsing to Vector by introducing a parseVectormethod that doesnt convert to List, and then calling that from a parsemethod returning List, to maintain compatiblity.

Happy to send a PR if you are open to this idea?

[tototoshi]

I think this is not so important from the point of view of performance, because the list of fields are not so long.
However, it was a big mistake to use List[String] as the type of interface. It has no reason to be List[String]. I will change it to Seq[String] and use Vector as implementation in the future.

[tototoshi]

#99