Logging to file, etc.
Enhancements when turning on OPENZGY_VERBOSE:
- Loggers are now aware of which open dataset they belong to
- Optionally log to file given by OPENZGY_VERBOSE_LOGFILE="myfile.log"
- Optionally add timestamps and dataset name / index with OPENZGY_VERBOSE_DETAILS=3
- Optionally log output from each dataset into a separate file, use {} plceholder in file name.