Fix broken links in the docs (line#783)

-
https://line.github.io/line-bot-sdk-nodejs/getting-started/basic-usage.html
- https://line.github.io/line-bot-sdk-nodejs/guide/client.html
- https://line.github.io/line-bot-sdk-nodejs/guide/webhook.html

---------

Co-authored-by: Yuta Kasai <[email protected]>

Author: tokuhirom

docs/api-reference.md

@@ -74,4 +74,4 @@ app.listen(3000);
 The full examples with comments can be found
 in [examples](https://github.com/line/line-bot-sdk-nodejs/tree/master/examples/).
 
-For the specifications of API, please refer to [API Reference](../api-reference.md).
+For the specifications of API, please refer to [API Reference](../apidocs/modules.md).

docs/getting-started/basic-usage.md

@@ -3,7 +3,7 @@
 Client is to send messages, get user or content information, or leave chats.
 A client instance provides functions for [messaging APIs](https://developers.line.biz/en/reference/messaging-api/),
 so that you do not need to worry about HTTP requests and can focus on data.
-For type signatures of the methods, please refer to [its API reference](../api-reference/client.md).
+For type signatures of the methods, please refer to [its API reference](../apidocs/modules.md).
 
 ## Create a client
 
@@ -124,5 +124,5 @@ stream.on('error', (err) => {
 ```
 
 You can check which method returns `Promise` or `ReadableStream` in the API
-reference of [`Client`](../api-reference/client.md). For type signatures of the
-errors above, please refer to [Exceptions](../api-reference/exceptions.md).
+reference of [`Client`](../apidocs/modules.md). For type signatures of the
+errors above, please refer to [Exceptions](../apidocs/modules.md).

docs/guide/client.md

@@ -15,16 +15,14 @@ of the official document.
 **Signature validation** is checking if a request is actually sent from real
 LINE servers, not a fraud. The validation is conducted by checking
 the [X-Line-Signature](https://developers.line.biz/en/reference/messaging-api/#signature-validation) header
-and request body. There is a [`validateSignature()`](../api-reference/validate-signature.md)
-function to do this.
+and request body. There is a `validateSignature()` function to do this.
 
 **Webhook event object parsing** is literally parsing webhook event objects,
 which contains information of each webhook event. The objects are provided as
-request body in JSON format, so any body parser will work here. For interal
-object types in this SDK, please refer to [Message and event objects](../api-reference/message-and-event-objects.md).
+request body in JSON format, so any body parser will work here.
 
 There is a function to generate a [connect](https://github.com/senchalabs/connect) middleware,
-[`middleware()`](../api-reference/middleware.md), to conduct both of them. If
+[`middleware()`](https://github.com/line/line-bot-sdk-nodejs/blob/master/lib/middleware.ts), to conduct both of them. If
 your server can make use of connect middlewares, such as [Express](https://expressjs.com/),
 using the middleware is a recommended way to build a webhook server.
 
@@ -115,7 +113,7 @@ However, there are environments where `req.body` is pre-parsed, such as
 [Firebase Cloud Functions](https://firebase.google.com/docs/functions/http-events).
 If it parses the body into string or buffer, the middleware will use the body
 as it is and work just fine. If the pre-parsed body is an object, the webhook
-middleware will fail to work. In the case, please use [`validateSignature()`](../api-reference/validate-signature.md)
+middleware will fail to work. In the case, please use [`validateSignature()`](https://github.com/line/line-bot-sdk-nodejs/blob/master/lib/validate-signature.ts)
 manually with raw body.
 
 ## Error handling
@@ -127,7 +125,7 @@ and the other is `JSONParseError`.
 - `SignatureValidationFailed` is thrown when a request has a wrong signature.
 - `JSONParseError` occurs when a request body cannot be parsed as JSON.
 
-For type references of the errors, please refer to [the API reference](../api-reference/exceptions.md).
+For type references of the errors, please refer to [the API reference](../apidocs/modules.md).
 
 The errors can be handled with [error middleware](https://github.com/senchalabs/connect#error-middleware).