= jsonob: JSON / Object Mapper

`marshal` from the stdlib allows you to serialize your arbitrary nim objects
into JSON strings and get your objects back from those serialized JSON strings.
But what if, you want to exchange data in JSON strings between Web APIs and your code?
`marshal` doesn't work any more because:

- It can't parse JSON `null` correctly.
- It can't serialize `Option[T]` properly (it just serialize all the fields of it, but it should really be `null` for `none(T)` and `value` for `some(value)`)
- It is designed for serialize *arbitrary* nim objects, instead of requiring you to model your nim objects around JSON.

That's where `jsonob` come in.
You model your nim objects directly around the JSON data.
`jsonob` serialize it to JSON, or parse the JSON to your objects.

== Example

----
import json, jsonob, options

type
    Result = object
        status: Status
        messages: seq[Message]
        error: Option[string]       # exists only when status == failed

    Status = enum
        ok
        failed

    Message = object
        `from`: Option[string]    # none for "anonymous"
        text: string
        date: Date

    Date = tuple
        year: int
        month: int
        day: int


proc test(s: string) =
    let r = s.parse_json.to Result

    case r.status
    of Status.ok:
        for message in r.messages:
            echo message.`from`
            echo message.text
            echo message.date
    of Status.failed:
        echo "failed"
        echo r.error.get()

    echo()

test """
{
    "status": "ok",
    "messages": [
        {
            "text": "hello world",
            "date": [2016, 7, 15]
        }
    ]
}
"""

test """
{
    "status": "failed",
    "messages": [],
    "error": "that's an error"
}
"""
----

.The output
----
None[string]
hello world
(year: 2016, month: 7, day: 15)

failed
that's an error

----

== TODO

* support for object variant

----
type
    Result = object
        case status: Status
        of Status.ok:
            messages: seq[Message]
        of Status.failed:
            error: string
----

* better error message
* documentation