Add :package-version to every defcustom

[bbatsov]

Last of the five improvements (the Codecov half of #5 already landed once you added the token). None of the 13 defcustoms carried a :package-version, so Customize couldn't say which release introduced each option and M-x customize-changed couldn't surface them on upgrade.

Adds :package-version '(helm-projectile . "X") to all 13, with the version for each derived from git archaeology (the first release tag whose history contains the option's introduction). Recent ones map to 1.6.0; the oldest to 0.14.0 / 1.0.0.

• The commits are consistent with our contribution guidelines
• The new code is not generating bytecode or M-x checkdoc warnings
• You've updated the changelog
• You've updated the readme (no user-facing change)

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.17%. Comparing base (865e58d) to head (08016bc).
⚠️ Report is 1 commits behind head on master.
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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #220   +/-   ##
=======================================
  Coverage   55.17%   55.17%           
=======================================
  Files           1        1           
  Lines         560      560           
=======================================
  Hits          309      309           
  Misses        251      251           

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