KSY (YAML) parser support for JSON
From http://doc.kaitai.io/ksy_reference.html#ksy-file

> KSY files
> 
> Kaitai Struct data structure (format) descriptions (KSY files) are simple YAML files and are usually saved using .ksy extension to differentiate them from the rest of .yaml files.
> 
> Every .ksy file MUST be a valid YAML file, and is expected to be parsed with generic YAML parsing libraries. Inside, every file MUST provide a map of strings (keys) to some values. Each file is essentially a single User-defined type spec.
> 

Relation to JSON

- https://en.wikipedia.org/wiki/JSON#YAML
- https://yaml.org/spec/1.2/spec.html#id2759572
- https://www.json.org/json-en.html

But currently JSON is not supported as input:

https://ide.kaitai.io/
> Kaitai WebIDE version: 0.1-SNAPSHOT-b2479d8 (2018-03-22 10:43:49, license)
> Kaitai compiler version: 0.8-SNAPSHOT337369088 (2018-02-05 01:36:23.722)
> 

This input

```
{
  "doc": "json test",
  "meta": {
    "id": "test",
    "endian": "le"
  },
  "seq": [
    {
      "id": "version",
      "contents": [
        1,
        255,
        255,
        255
      ],
      "doc": "4 - structure version"
    }
  ]
}
```

causes this error

```
Parse error (Error): Unexpected characters (
  },
  "seq": [
    {
      "id": "version",
      "contents": [
        1,
        255,
        255,
        255
      ],
      "doc": "4 - structure version"
    }
  ]
}).
Call stack:  <ParseException> Unexpected characters (
  },
  "seq": [
    {
      "id": "version",
      "contents": [
        1,
        255,
        255,
        255
      ],
      "doc": "4 - structure version"
    }
  ]
}). (line 1: '{')
```
