Add more documentation to CSVPrinter

CSVPrinter has almost no class level documentation. We should write some docs including usage examples.

Furthermore we discussed to document the inconsistent line ending/record separator behavior especially when calling CSVPrinter.printComment(String) (see https://lists.apache.org/thread.html/b493c4e461a5218995eeac7932b30498484d798afed9cc31870e98e6@%3Cdev.commons.apache.org%3E )