Hi Jack, thanks for this fine library! I recently wrote decoder DCF77 library (for the atomic time broadcasted by the DCF77 radiostation) (see this thread) which now includes an example of usage together with your TimeZone library.
Before I read the TimeZone README I had not considered that converting from local time to UTC is ambiguous in the hour before switching to winter time. Luckily for us DCF77 users, the DCF77 data package includes info about DST, so in the latest version I added a function to the library that unambiguously converts CET to UTC time.