Finally deprecate the legacy line-based format

[tianon]

Closes #16

(This is the real reason behind #44 😂 wanted an easier way to see whether this actually decreases coverage anywhere that matters 👀)

[codecov-commenter]

Codecov Report

Merging #45 (69f4323) into master (017573e) will decrease coverage by 1.52%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #45      +/-   ##
==========================================
- Coverage   78.35%   76.83%   -1.53%     
==========================================
  Files           7        5       -2     
  Lines         670      587      -83     
==========================================
- Hits          525      451      -74     
+ Misses        110      104       -6     
+ Partials       35       32       -3     

Impacted Files	Coverage Δ
manifest/rfc2822.go	73.14% <ø> (-1.44%)	⬇️

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[tianon]

I've reviewed the "change in coverage" lines from https://app.codecov.io/gh/docker-library/bashbrew/compare/45/changes and they're all reasonable! I think my naive approach to removing this is probably correct. 😄

[tianon]

$ ./bin/bashbrew cat --all > /dev/null
$ 

🎉

(No current manifests use the line-based format thanks to the work in #16)