serializers are inherited. Streams can't be removed as part of the child
creation. The child doesn't own the parent's streams (so can't close them).
- Clean up Logger creation. The goal here was to ensure `log.child` usage
is fast. TODO: measure that.
- Add `Logger.stdSerializers.err` serializer which is necessary to get good
Error object logging with node 0.6 (where core Error object properties
are non-enumerable).
