diff between two references on the same branch

[nopcoder]

Closes #603

[arielshaqed]

Thanks!

Discussed f2f with @nopcoder and decided to push an unrelated change (which I don't understand so cannot approve) in a separate PR.

[codecov-io]

Codecov Report

Merging #842 into master will increase coverage by 1.29%.
The diff coverage is 72.38%.

@@            Coverage Diff             @@
##           master     #842      +/-   ##
==========================================
+ Coverage   43.09%   44.39%   +1.29%     
==========================================
  Files         136      137       +1     
  Lines       10648    10587      -61     
==========================================
+ Hits         4589     4700     +111     
+ Misses       5461     5277     -184     
- Partials      598      610      +12     

Impacted Files	Coverage Δ
catalog/db.go	81.81% <ø> (+1.58%)	⬆️
catalog/cataloger_diff.go	67.56% <72.13%> (+0.90%)	⬆️
catalog/cataloger_merge.go	61.78% <75.00%> (+0.97%)	⬆️
api/handler.go	70.52% <0.00%> (ø)
api/client.go	4.65% <0.00%> (+1.14%)	⬆️

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[arielshaqed]

Thanks!
StilLGTM.