[Feature] implement function json_getString
[Feature] implement function json_getNumber
[Featrue] implement function json_getBoolean
[Feature] implement function json_getNull
[Feature] implement function json_getValue

* Find JSON Object and Array in shallow

  (only get the left and right bracket, but do not check inside)
[Refactor] implement internal function json_getShallowObject and json_getShallowArray