Support multiple values for JSON PATH

[niusounds]

Related #197

I want to get user ids from this response:

{
  "payload": {
    "results": [
      {
        "user": {
          "id": "aaa",
          "name": "alice",
          "iconUrl": "https://foo/bar"
        },
        "isFollowed": false,
        "isFollowing": true
      },
      {
        "user": {
          "id": "bbb",
          "name": "alice",
          "iconUrl": "https://foo/bar"
        },
        "isFollowed": false,
        "isFollowing": true
      },
      {
        "user": {
          "id": "ccc",
          "name": "alice",
          "iconUrl": "https://foo/bar"
        },
        "isFollowed": false,
        "isFollowing": true
      }
    ]
  }
}

with

@userIds = {{search.response.body.$..user.id}}

expected result is ["aaa","bbb","ccc"] (string). So I can send userIds with next request

POST some/api

{
  "userIds": {{userIds}}
}

Works as usual if JSON path is matching to only one element.

[evanportwood]

@Huachao is there any possibility of getting this PR completed? This would be really helpful!