Enforce using non-blocking I/O

[clue]

Opening this an RFC, any input is welcome! 👍

Reading from a stream should never block the loop.
This is known to be an issue for process pipes on Windows.

Refs: reactphp/child-process#9 and reactphp/reactphp#68

[clue]

The following gist can be used to reproduce this issue:

$loop = React\EventLoop\Factory::create();

// dummy timer to see some activity on STDOUT
$loop->addPeriodicTimer(1.0, function () {
    echo microtime(true) . PHP_EOL;
});

// this will always return false on Windows
var_dump(stream_set_blocking(STDIN, false));

$loop->addReadStream(STDIN, function () {
    // this will always block on Windows
    fread(STDIN, 1024);
});

$loop->run();

See https://bugs.php.net/bug.php?id=47918 for details, there does not appear to be a way to circumvent this in PHP.

[clue]

Rebased on current master and added tests to ensure 100% coverage using a stream wrapper

[jsor]

@clue Tests on hhvm are failing.

React\Tests\Stream\EnforceBlockingWrapper::stream_cast is not implemented!

[clue]

Thanks for spotting, updated to fix tests on HHVM