Add errors for incorrect newlines

[pezholio]

As per the discussion with @JeniT in the last PR, the RFC for CSVs specifically says that lines 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.

[pezholio]

@JeniT - All done now! 😄

[coveralls]

Coverage remained the same when pulling e55ffa5 on feature-detect-newline-types into b495b5b on master.