Alexa APLのPager

Ref: https://developer.amazon.com/ja/docs/alexa-presentation-language/apl-pager.html

- firstItem -> itmes -> lastItemの順番で表示される（多分）
- initialPage（0からはじまる）を使うことでスタート位置を調整可能。
- navigationを`forward-only`にすると、一方通行にできる


## sample
```
{
    "type": "APL",
    "version": "1.0",
    "theme": "dark",
    "import": [
        {
            "name": "alexa-layouts",
            "version": "1.0.0"
        }
    ],
    "resources": [],
    "styles": {},
    "layouts": {
        "cover": {
            "parameters": [{
                "type": "string",
                "name": "lead"
            }],
           "item": [
               {
                   "type": "Container",
                   "width": "100vw",
                   "height": "100vh",
                   "alignItems": "center",
                   "justifyContent": "center",
                   "items": [
                       {
                           "type": "Text",
                           "text": "${lead}"
                       }
                    ]
               }
            ] 
        },
        "myFirstLayout": {
            "parameters": [
                {
                    "name": "title",
                    "type": "string"
                },{
                    "name": "subTitle",
                    "type": "string"
                },{
                    "name": "imageUrl",
                    "type": "string"
                },{
                    "name": "hint",
                    "type": "string"
                }
            ],
            "item": [
                {
                    "type": "Container",
                    "direction": "row",
                    "alignItems": "center",
                    "justifyContent": "spaceBetween",
                    "height": "100vh",
                    "width": "100vw",
                    "items": [
                        {
                            "type": "Container",
                            "width": "50vw",
                            "alignItems": "center",
                            "justifyContent": "center",
                            "items": [
                                {
                                    "type": "Text",
                                    "text": "${title}",
                                    "fontSize": "100dp"
                                }, {
                                    "type": "Text",
                                    "text": "${subTitle}"
                                }
                            ]
                        }, {
                                "scale": "best-fill",
                                "width": "50vw",
                                "height": "100vh",
                                "type": "Image",
                                "source": "${imageUrl}"
                        }
                    ]
                }
            ]
        }
    },
    "mainTemplate": {
        "parameters": ["payload"],
        "items": [
            {
                "type": "Pager",
                "width": "100vw",
                "height": "100vh",
                "navigation": "forward-only",
                "initialPage": 0,
                "firstItem": [
                    {
                        "type": "cover",
                        "lead": "Welcome to the skill"
                    }
                ],
                "lastItem": [
                    {
                        "type": "cover",
                        "lead": "See you !"
                    }
                ],
                "items": [
                    {
                      "type": "myFirstLayout",
                      "title": "Hello",
                      "subTitle": "${payload.examplePayload.subTitle}",
                      "hint": "${payload.examplePayload.hint}",
                      "imageUrl": "${payload.examplePayload.imageUrl}"
                    },
                    {
                      "type": "myFirstLayout",
                      "title": "How are you?",
                      "subTitle": "${payload.examplePayload.subTitle}",
                      "hint": "${payload.examplePayload.hint}",
                      "imageUrl": "${payload.examplePayload.imageUrl}"
                    }
                ]
            }
        ]
    }
}
```

ネプリーグのトロッコアドベンチャーみたいなことも頑張ればできそう（適当）。