Provide access methods for header and trailer comments

The Apache Commons CSV library can deal with comments by attaching the comment to the following record.
It does not seem possible to access comments that are before the header line ("header comments"), or after the last record ("trailer comments")
I feel this would be a useful enhancement to the current comment-handling features of version 1.9.

I have not been able to find mention of this in other JIRA tickets.

I have attached a patch implementing this, for discussion purposes. (n.b. I had trouble with git showing spurious ^M at the end of changed lines in CSVParserTest.java which I could not get rid of)

This adds methods String CSVParser::getHeaderComment(), String CSVParser::getTrailerComment(), bool CSVParser::hasHeaderComment() and bool CSVParser::hasTrailerComment() . The last two could be omitted assuming a missing comment would return a null String.

See also https://stackoverflow.com/questions/72619095/get-leading-comments-from-csv-with-apache-commons-csv and https://lists.apache.org/thread/8tczpqlnjgbcyovyhb484tt11vqv91jt