Add errors for incorrect newlines

As per the discussion with @jenit in the last PR, the [RFC for CSVs](http://tools.ietf.org/html/rfc4180) specifically says that li
nes should be specified as `/r/n` (or `CRLF` as the docs state). This PR does two things:

* Returns an error if newlines are explicitly set to anything other than `/r/n`
* Returns an error if newlines are left as the default (the parser will choke in this case), and `/n` is detected in the row

Should be all good to go, but I'd appreciate some feedback first.