Parser: Escaped quote in unquoted value must throw.

[ImrePyhvel]

5. Each field may or may not be enclosed in double quotes (however
   some programs, such as Microsoft Excel, do not use double quotes
   at all). If fields are not enclosed with double quotes, then
   double quotes may not appear inside the fields.

Repro steps: add 2 consecutive quotes within a value during parsing (Ex: my""value)
Current behavior: current parser (0.9.2) considers it an escaped quoting char (Ex: my"value)
Expected behavior: By RFC it must be invalid input instead. Exceptions should be thrown stating invalid input.

While current implementation can successfully parse wider range of documents, it is in conflict with RFC4180. As compliance is a main goal for the project then it can be considered a bug.

Added test TestUnquotedValueContaining2QuotesThrows to repro the issue.