add archive by date and by tag

I tried mimicking this https://chadbaldwin.net/archive.html in commit [bc1cbadad08282c7e342645d01065ded1302bb8b](https://github.com/famulare/famulare.github.io/commit/bc1cbadad08282c7e342645d01065ded1302bb8b) but it didn't work, presumably because I missed something I don't understand.