request and response log

[kortemik]

I am willing to make a PR for request and response log feature.

Would it be preferred that one adds:

1. A separate handler in addition to S3ProxyHandlerJetty like Jetty describes for NCSA at https://www.eclipse.org/jetty/documentation/jetty-9/index.html#configuring-jetty-logging

2. Modifies the S3ProxyHandlerJetty so that it takes a logging class implementatation as argument and modify S3Proxy so it has setLogger() which passes the logging class implementatation to S3ProxyHandlerJetty? The default would be a no-op final class which gets optimized out.

[gaul]

One simple implementation would to be to add logger.trace calls for the request and response codes and headers. What value does a logger class provide?

Duplicate of #213?

[kortemik]

Logger class provides the ability to log needed headers and such, of course we could change that the logger.trace outputs them all as json but it may be too much for request log.