Added metadata option to return column type and charsets

This PR adresses #39

It basically adds an option `metadata` when connection. If metadata is set to true, an additional argument will be emitted for each row, containing column type and charset. I would really like to provide some kind of test / proof that this works, but the repo doesn't seem to have any tests? One proof would be that I have used the changes to implement mariadb support in sequelize/sequelize#948, and all tests pass (including tests that BLOBs, Dates, ints etc. are returned as their proper js data types)