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

test/unit/api.test.js

@@ -135,7 +135,7 @@ test('Abort method (callback)', t => {
   })
 })
 
-test('Abort is not supported in promises', t => {
+test('Abort method (promises)', t => {
   t.plan(2)
 
   function handler (req, res) {
@@ -160,7 +160,7 @@ test('Abort is not supported in promises', t => {
       })
       .catch(t.fail)
 
-    t.type(request.abort, 'undefined')
+    t.type(request.abort, 'function')
   })
 })