Provided stacktraces for lua errors

[RustyBlade64]

When a runtime error happens while executing lua code only the error, but no stacktrace is displayed. It would be a nice convenience feature if that could be added.

I know this strictly doesn't belong here, but your golua repository does not have issues enabled (due to being forked I believe) and the original project seems inactive, so I thought I'd put it here.

For reference this has also been reported at aarzilli/golua#58