Need to add `format:"json"` tag

[elias506]

In method messages.send need to add format:"json" tag to fields messages_forward and messages_keyboard:

{
        "name": "messages.send",
        ...
        "parameters": [
                ...
                {
                  "name": "forward",
                  "description": "JSON describing the forwarded message or reply",
                  "type": "string",
                  "format": "json",
                  "$ref": "objects.json#/definitions/messages_forward"
                },
                ...
                {
                  "name": "keyboard",
                  "type": "string",
                  "format": "json",
                  "$ref": "objects.json#/definitions/messages_keyboard"
                },
                ...
}

[elias506]

Fix by #214