Add a comment about $this->_node.
Implement the `broadcastIf` method.

This method broadcasts a message to a subset of nodes that respect a
given predicate. For example:

    $source->broadcastIf(
        function ( \Hoa\Socket\Node $node ) {

            return $node->getNumber() > 5;
        },
        'You are high!'
    );
Fix setEncryption issue for multiple client.
PR #6 | Move encryption to Hoa\Socket\Node
PR #6 | Fix erase declaration
PR #6 Rename encryption to encrypted
PR #6 | Rename function & change default flag type to null
PR #6 | Fix enableEncryption()
PR #6 | Fix rename property
PR #6 | Rename Connection::getEncryption() to getEncryptionType()
PR #6 | fix null instead false
PR #6 | Optimize Connection::enableEncryption
PR #6 | Rename Connection::getEncryptionType into Connection::isEncrypted
PR #6 | Fix null equal & reinsert in if/else condition
PR #6 Fix minor syntax write
Fix CS and API documentation.
Update comment of Node::setEncryptionType()