Better error handling / logging

[jerrypnz]

There are a lot of places where exceptions are caught and logged using printStackTrace or System.err.println. It's not ideal for production systems where errors are generally written to log files instead of stderr.

Would be great if they can be replaced with an actual logger like slf4j, or maybe it should always bubble up exceptions to the caller and leave it to them to decide how exceptions should be handled.

If you think it's a good idea, we have a patch which replaces printStackTrace and System.err.println with slf4j Logger.error.