Refactor csv reader

Readers should be functions:
[String] -> Series a

or maybe
[String] -> [DataPoint]

It should be easy to add to the reader transformation to change file with content like in Fix Daily__Dec-18-2016_09_42_43AM.csv into TimeSeries

And also csv with more then 2 columns

The issue names no files or tests; begin by locating the current CSV reader and the definitions of Series, DataPoint, and TimeSeries. Clarify the intended function signature, transformation path, and handling of CSVs with more than two columns before defining what completion means.

Written by the indexing model from the issue text.