pretty print on json export

[telephon]

It would be nice to have JSONLib produce better formatted JSON files – a pretty print formatting would be what is needed for this.

javascript has a space parameter for this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#using_the_space_parameter

https://github.com/douglascrockford/JSON-js/blob/master/json2.js