Merge: StatementRow::map

I thought this was lacking from the API, so now when dealing with a StatementRow, one can get a map from column name to column value.

NOTE: This is not lazy since Sqlite re-uses the StatementRow for each row returned when a select statement is sent to the database.

Pull-Request: #2308
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>