Uploading files individually to Dropbox is flaky, and the unique URL per
file complicates data/MANIFEST.
While we're at it, start carving aside a directory structure for keeping
data for the last few releases.
[rebuild] to make sure github actions can download everything
intersection polygon in Krakow that has really bad geometry, and this
improves it. The extra check absolutely shouldn't be necessary, but of
course, all the core line intersection code is quite suspect! #161
Also gets rid of some annoying warnings about roads with missing names.
I could continue to skip the warning for more situations, but I think
this sort of data quality check could be done better in the OSM viewer.
showed this is faster than downloading the uncompressed files, but of
course it probably depends on network speed vs CPU. #326
Also cut over the updater to use gzipped files using flate, instead of
single-file .zip's. [rebuild]
