run Plack::Test on AnyEvent-based PSGI applications

 Plack::Test::AnyEvent allows you to easily test
 your AnyEvent-based PSGI applications.
 Normally,
 Plack::Test::MockHTTP or Plack::Test::Server work fine for this,
 but this implementation comes in handy
 when you'd like to test your streaming results as they come in,
 or if your application uses long-polling.
 For non-streaming requests,
 you can use this module exactly like Plack::Test::MockHTTP;
 otherwise, you can set up a content handler and call $res->recv.
 The event loop will then run
 until the PSGI application closes its writer handle
 or until your test client calls send on the response.