Replace elseifs with early returns in Connection

[jeromegamez]

This PR proposes replacing all elseif branches in the generated Connection class with early returns.

This is in preparation for #152, which has the primary goal of removing a duplicate check

bunny/src/Connection.php

Lines 342 to 347 in 873ec47

	if ($frame instanceof Protocol\MethodConnectionCloseFrame) {
	return true;
	} elseif ($frame instanceof Protocol\MethodConnectionCloseFrame) {
	$this->connectionCloseOk();
	throw new ClientException($frame->replyText, $frame->replyCode);
	}

The problem there is that this requires removing an if branch and converting an elseif branch to an if branch.

Removing elseif branches in the first place will make this a lot easier.

[WyriHaximus]

Great work, thank you for putting this together 👍