tobgu/qframe

📋 Changes

• 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
• 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