Embedded newlines and empty string fixes + tests

Hi, I have crunched a fair amount of data using csv-parser and kept patching it with each new quicklisp install/update. I have finally fixed some issues that have been nagging me.

I believe the way embedded newlines should be handled, as implied/embodied in the existing test is not working, and have fixed it.

Not sure the empty strings patch is in keeping with any specs as such, but seems reasonable compared to other csv tools like database imports etc (and round trips well now).

The only style still not quite looking right to me is that the test cases appear before the output/write functions, so the tests forward reference the function(s) being tested.

By the way, it also appears to me that csv-parser is the fastest out there. Would definitely still like something faster, processing large amounts of data requires speed, csv-parser is cpu limited at the moment.