Re: [tz] Expanding the section on the Czech Republic and Slovakia

Thanks for the citations and the readings of sources. They agree with what's currently in TZDB except for the 1918 transitions, which TZDB and the main text of "Kdy začíná a končí letní čas" both say occurred at the usual times, whereas the 1918 source cited by "Kdy začíná a končí letní čas" says the transitions occurred an hour earlier than usual. The 1918 source seems to be full of Czech humor so I tend to think it's not as reliable as we'd like. For now I installed the attached patch to the TZDB commentary, to mention the discrepancy but without changing the data proper. We can of course adjust the data later if we find better sources. Admittedly it is hard to find good sources for central Europe in 1918.