Add --rev option to allow for bundle revisions

[gamebox]

This is related to #753

[codecov-io]

Codecov Report

Merging #756 into master will decrease coverage by 0.23%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master     #756      +/-   ##
==========================================
- Coverage   94.35%   94.11%   -0.24%     
==========================================
  Files          64       64              
  Lines        2036     2040       +4     
==========================================
- Hits         1921     1920       -1     
- Misses        115      120       +5

Impacted Files	Coverage Δ
src/Bundler.js	91.48% <ø> (ø)	⬆️
src/packagers/Packager.js	81.25% <60%> (-10.42%)	⬇️
src/assets/CSSAsset.js	82.35% <0%> (-7.36%)	⬇️
src/Logger.js	96.96% <0%> (+1.51%)	⬆️
src/WorkerFarm.js	93.22% <0%> (+1.69%)	⬆️

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[lbguilherme]

1. I don't think this behavior need to be behind a flag. Is there a downside of always adding the hash?
2. The outer bundle probably shouldn't have hash, as it is referred by name (the index.html).
3. RawPackager needs work too, as it doesn't use setup from Packager.

[devongovett]

Should be solved by #1025 which generates content-hashed filenames for static assets. Please help test using the master branch - a release will hopefully come next week!