Make generating stack traces (Exception.toString()) in the HTTP server optional.

The new HTTPServerOption.errorStackTraces option is used to control this behavior. Stack traces are enabled by default for backwards compatibility reasons.
Make logging arguments lazy to avoid evaluating costly log message arguments when not necessary.

In particular, calling the costly Exception.toString() method, which is often used in debug messages to provide extended exception information, is to be avoided when the minimum log level doesn't include debug messages.