Add new request() and requestStreaming() methods and deprecate send() method and streaming option

[clue]

This changeset introduces two new methods, request() and requestStreaming().

The request() method can be used to send arbitrary HTTP requests and deprecates the send() method:

// old: deprecated
$browser->send(new Request('OPTIONS', $url));

// new
$browser->request('OPTIONS', $url);

The requestStreaming() method can be used to send an arbitrary HTTP request and receive a streaming response without buffering the response body:

// old: deprecated
$browser->withOptions(['streaming' => true])->get($url);

// new
$browser->requestStreaming('GET', $url);

Refs #154 and #56 and others.
Builds on top of #162, #167 and #168