Add resolveAll() method to support custom query types in Resolver

[clue]

This PR adds a new resolveAll($domain, $type) method which supports sending custom query types, such as AAAA queries. This allows you to query all known query types (see #31) and is also the prerequisite for IPv6 lookups in our Socket component (reactphp/socket#116) as discussed in #43.

$resolver->resolveAll('reactphp.org', Message::TYPE_A)->then(function ($ips) {
    echo 'IPv4 addresses for reactphp.org ' . implode(', ', $ips) . PHP_EOL;
});

$resolver->resolveAll('reactphp.org', Message::TYPE_AAAA)->then(function ($ips) {
    echo 'IPv6 addresses for reactphp.org ' . implode(', ', $ips) . PHP_EOL;
});

Supersedes / closes #67, thank you @WyriHaximus!
Resolves / closes #43
Builds on top of #109