Updated abort behavior (#1141)

* Updated abort behavior

- Support for aborting a request with the promise api
- Aborting a request will cause a RequestAbortedError
- Normalized Connection class errors, now every error returned is
wrapped by the client errors constructors

* Updated test

* Updated docs

* Updated code generation script

* Renamed test

* Code coverage

* Avoid calling twice transport.request

docs/usage.asciidoc

@@ -67,45 +67,34 @@ client.search({
 
 === Aborting a request
 
-When using the callback style API, the function also returns an object that 
-allows you to abort the API request.
+If needed, you can abort a running request by calling the `request.abort()` method returned by the API.
+
+CAUTION: If you abort a request, the request will fail with a `RequestAbortedError`.
 
 
 [source,js]
 ----
-// calback API
 const request = client.search({
   index: 'my-index',
   body: { foo: 'bar' }
 }, {
   ignore: [404],
   maxRetries: 3
-}, (err, { body }) => {
-  if (err) console.log(err)
+}, (err, result) => {
+  if (err) {
+    console.log(err) // RequestAbortedError
+  } else {
+    console.log(result)
+  }
 })
 
 request.abort()
 ----
 
-Aborting a request with the promise style API is not supported, but you can 
-achieve that with convenience wrapper.
-
+The same behavior is valid for the promise style API as well.
 [source,js]
 ----
-function abortableRequest (params, options) {
-  var request = null
-  const promise = new Promise((resolve, reject) => {
-    request = client.search(params, options, (err, result) => {
-      err ? reject(err) : resolve(res)
-    })
-  })
-  return {
-    promise,
-    abort: () => request.abort()
-  }
-}
-
-const request = abortableRequest({
+const request = client.search({
   index: 'my-index',
   body: { foo: 'bar' }
 }, {
@@ -113,8 +102,11 @@ const request = abortableRequest({
   maxRetries: 3
 })
 
+request
+  .then(result => console.log(result))
+  .catch(err => console.log(err)) // RequestAbortedError
+
 request.abort()
-// access the promise with `request.promise.[method]`
 ----
 
 
@@ -213,6 +205,9 @@ You can find the errors exported by the client in the table below.
 |`ConnectionError`
 |Generated when an error occurs during the request, it can be a connection error or a malformed stream of data.
 
+|`RequestAbortedError`
+|Generated if the user calls the `request.abort()` method.
+
 |`NoLivingConnectionsError`
 |Given the configuration, the ConnectionPool was not able to find a usable Connection for this request.