SQL and plotting support! Thanks a lot to @kevinschoon for adding this!

• Add support for reading from/writing to SQL databases. Thanks @kevinschoon for this!
• Add support for plotting using Gonum plot. Thanks @kevinschoon for this!
• Rename ToJson/FromJson/ToCsv/FromCsv -> ToJSON/FromJSON/ToCSV/FromCSV for
  consistency with stdlib. Thanks @sbinet for this!
• qframe.Expr1 and qframe.Expr2 have been merged to one function qframe.Expr.
• Minor bug fix in CSV reading where reads that return io.EOF together with
  data previously did not work.

Initial release