Simplify usage by supporting new default loop

[clue]

This changeset simplifies usage by supporting the new default loop.

// old (still supported)
Clue\React\Block\await($promise, $loop);
Clue\React\Block\awaitAny($promises, $loop);
Clue\React\Block\awaitAll($promises, $loop);

// new (using default loop)
Clue\React\Block\await($promise);
Clue\React\Block\awaitAny($promises);
Clue\React\Block\awaitAll($promises);

Builds on top of reactphp/event-loop#226 and reactphp/http#410
Builds on top of #59