Add CSVReader class in `CSV` folder

[peter279k]

In addition to the CSVWriter class, I think we can add the CSVReader class in the CSV folder.

[acoulton]

That's a good idea - we have a few variations lying around in different projects, we'll look at extracting one. Or if you wanted to contribute one (with tests) we'd be happy to look at taking that.

Needs obviously to cope with (/throw on) things like mismatched numbers of columns on a row, and should iterate rows one at a time rather than reading the whole file into memory. Also needs to continue reading to the end of the file even if there's a completely empty line.