Add exist | not exist to leaf types

[code-is-art]

I needed it for my project and added it to my git clone of this project so I can do the following...

{
  "$or": [
    {
      "payload.fileInfo.size": {
        "$exists": true
      }
    },
    {
      "payload.fileInfo.size": {
        "$gt": "12345"
      }
    }
  ]
}

Every leaf type has an opr: exist | not exist and I removed the deprecated opr. I think its a good feature to have for people.