for escaping the value delimiter rather than the delimiter value
  appearing twice.

* CsvReader.cs: Support passing the EscapeCharacter down to the
  CsvParser.

* CsvParser.cs:
* CsvParser_Async.cs: Added property to specify an escape character to
  use for handling the delimiter character appearing within the value.
  When specified this character will act as an escape character rather
  than needing to have the delimiter character twice. e.g. setting \
  as the escape character would support escaping values like "some
  \"quoted\" text" rather than "some ""quoted"" text".