lib:
- handle checkout of trees which contain submodules by identifying and
  ignoring such tree entries; requires a .ini config parser (from isakmpd?)
- fix 'got log -l1 -c fb4d85023675bc7da402da96b2bb84fd12905dbf -p';
  this command runs too slow in got-read-pack
  (maybe let got-read-pack cache ref/offset delta objects in object_cache.c?)
  commit fb4d85023675bc7da402da96b2bb84fd12905dbf is:
      from: jsg <jsg@openbsd.org>
      date: Wed May 22 00:40:06 2019 UTC
      "add amdgpu from linux 4.19.44 for recent AMD Radeon parts"
- improve performance of usr.bin/diff and port these changes back to got
  (e.g. diffing between versions of sys/dev/pci/pcidevs is too slow)

got:
- 'histedit -c' prompts for log message even if there are no changes to commit
- recursive addition: got add -R
- recursive removal: got rm -R
- add 'got stage' command with 'git add -p' style functionality
- add 'got unstage' command to undo effects of 'got stage'
- add 'git checkout -p' style functionality to 'got revert' and 'got unstage'

tog:
- implement horizonal scrolling in all views
- implement horizonal split view mode
- implement search feature for diff view
- implement 'limit' for 'tog log' (like search but display matched commits only)
- allow moving to prev/next blamed line in diff view if opened from blame view,
  similar to how the diff view can switch commits if opened from log view
- tog should have a command to list and log/browse references