New 'wendelin.core' version contains several bugfixes that were
discovered in field usage. Furthermore it introduces the new 'ZBlk_fmt'
option 'auto' that heuristically sets ZBlkfmt to gain a good ratio between
read time and database size, improves python3 compatibility and synchronizes
NEO zurl scheme between NEO/py and NEO/go.

See nexedi/wendelin.core@63153845...db6fea3d
for complete list of changes.

/reviewed-by @kirr @jerome
/reviewed-on nexedi/slapos!1620