Additional csv option for quote_char

This will allow users to configure a different quoting char in cases where the data may not exactly fit the csv standard.

A common example may be to completely ignore the quote char, and to do this a null \x00 char can be used instead.
Another example may be csv with ' as the quote char instead of "
Add test for default csv quote_char double quote "
Merge pull request #725 from markabey/csv_quote_char

Csv quote char
Merge git://github.com/logstash/logstash