Add IDataReader implementation

[VitaliyMF]

In some cases it might be useful to read CSV stream as System.Data IDataReader. This unlocks simple way to read CSV to DataTable or to list of POCO-models - say, this is possible with DataReaderResult class from NReco.Data library.

In the initial implementation, lets expose all CSV line fields as 'string' FieldType, and add option to skip first (headers) line.