Refactored type definitions (#1119)

* Updated types generation script

* Refactored api method definitions

* Updated test
- Removed old test code
- Added tsd dev dependency
- Rewritten test with tsd

* Removed unused dependencies

* Fixed definition

* Updated test

* Updated docs

* Improved events type definitions

* Updated test

* Minor fixes in the type definitons

* More type test

* Improved Transport type definitions

* Updated test

* Addressed comments

* Code generation

* Use RequestBody, Response and Context everywhere, also default Context to unknown

* Updated test

* body -> hasBody

* Fixed conflicts

* Updated code generation

* Improved request body type definition

* Updated code generation

* Use BodyType for both request and reponses generics
- Use extends for defining the RequestBody generic to force the user
  following the same shape.
- BodyType and NDBodyType now accepts a generics to allow injecting
  more specific types in the future

* API generation

* Updated test

* Updated docs

* Use BodyType also in ReponseError

* Removed useless client generics

* Renamed generics and types
- prefixed all generics with a T
- BodyType => RequestBody
- NDBodyType => RequestNDBody
- Added ResponseBody

* Updated test

* Updated docs

* Test ResponseBody as well

* Simplify overloads

* API generation

* Updated test

* Updated error types

lib/errors.d.ts

@@ -2,7 +2,7 @@
 // Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information
 
-import { ApiResponse } from './Transport'
+import { ApiResponse, ResponseBody } from './Transport'
 
 export declare class ElasticsearchClientError extends Error {
   name: string;
@@ -33,8 +33,8 @@ export declare class NoLivingConnectionsError extends ElasticsearchClientError {
 export declare class SerializationError extends ElasticsearchClientError {
   name: string;
   message: string;
-  data: object;
-  constructor(message: string, data: object);
+  data: any;
+  constructor(message: string, data: any);
 }
 
 export declare class DeserializationError extends ElasticsearchClientError {
@@ -54,8 +54,8 @@ export declare class ResponseError extends ElasticsearchClientError {
   name: string;
   message: string;
   meta: ApiResponse;
-  body: any;
+  body: ResponseBody;
   statusCode: number;
-  headers: any;
+  headers: Record<string, any>;
   constructor(meta: ApiResponse);
 }