Ability to chain extraction functions to expand their functionality

[vogievetsky]

Function composition is cool.

In Plywood/PlyQL

SELECT CONCAT('[', SUBSTR(`language`, 0, 3), ']') AS "Crazy" FROM `wikipedia` GROUP BY 1

Something like:

{
  "type": "extraction_cascade",
  "dimension": "language",
  "outputName":  "Crazy",
  "extractionFns": [
    {
      "type": "substr",
      "index": 0,
      "length": 3
    },
    {
      "type": "concat",
      "prefix": "[",
      "postfix": "]"
    }
  ]
}