obshashrange: introduce basic sqlite caching
Same as for stablerange, this is far from perfect but already a win.
The cache is currently extremely volatile, but that will still be a win when
doing multiple consecutive request during discovery.
Better cache invalidation will happens "in the future".
syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes