Fix minor errors and doc comments (#2120)

* Fix minor errors and doc comments

* 2 anonymous functions were declaring using a variable that wasn't
used in the end, so this has been removed
* The 'delay' field of RetryMiddleware was not declared
* new TransferStats was called with 0 instead of null
* incorrect type was supplied to withHeader()
* various DocComments fixes

* revert back to 0

src/Cookie/CookieJar.php

@@ -120,7 +120,7 @@ public function clear($domain = null, $path = null, $name = null)
         } elseif (!$path) {
             $this->cookies = array_filter(
                 $this->cookies,
-                function (SetCookie $cookie) use ($path, $domain) {
+                function (SetCookie $cookie) use ($domain) {
                     return !$cookie->matchesDomain($domain);
                 }
             );

src/Handler/StreamHandler.php

@@ -42,7 +42,7 @@ public function __invoke(RequestInterface $request, array $options)
             // Append a content-length header if body size is zero to match
             // cURL's behavior.
             if (0 === $request->getBody()->getSize()) {
-                $request = $request->withHeader('Content-Length', 0);
+                $request = $request->withHeader('Content-Length', '0');
             }
 
             return $this->createResponse(

src/HandlerStack.php

@@ -206,7 +206,7 @@ public function resolve()
     }
 
     /**
-     * @param $name
+     * @param string $name
      * @return int
      */
     private function findByName($name)
@@ -223,10 +223,10 @@ private function findByName($name)
     /**
      * Splices a function into the middleware list at a specific position.
      *
-     * @param          $findName
-     * @param          $withName
+     * @param string   $findName
+     * @param string   $withName
      * @param callable $middleware
-     * @param          $before
+     * @param bool     $before
      */
     private function splice($findName, $withName, callable $middleware, $before)
     {

src/Middleware.php

@@ -58,7 +58,7 @@ public static function httpErrors()
                     return $handler($request, $options);
                 }
                 return $handler($request, $options)->then(
-                    function (ResponseInterface $response) use ($request, $handler) {
+                    function (ResponseInterface $response) use ($request) {
                         $code = $response->getStatusCode();
                         if ($code < 400) {
                             return $response;

src/RetryMiddleware.php

@@ -19,6 +19,9 @@ class RetryMiddleware
     /** @var callable */
     private $decider;
 
+    /** @var callable */
+    private $delay;
+
     /**
      * @param callable $decider     Function that accepts the number of retries,
      *                              a request, [response], and [exception] and
@@ -42,7 +45,7 @@ public function __construct(
     /**
      * Default exponential backoff delay function.
      *
-     * @param $retries
+     * @param int $retries
      *
      * @return int
      */