Require pipescripts to use CommonJS format

[ewindisch]

Implement a CommonJS compatible format for pipescripts, allowing them to be imported and used directly via NodeJS.

Simply define module.export as a function which receives input from the previous function. Example:

    module.exports = function(input) {
      var data = JSON.decode(input)
      return data['extract_this_field']
    }

[ewindisch]

Needs updated docs.