feat(policy): add policy enforcement; enforce git commit policy

[codecov[bot]]

Codecov Report

Merging #17 into master will decrease coverage by 13.5%. The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #17       +/-   ##
==========================================
- Coverage   20.75%   7.24%   -13.51%     
==========================================
  Files           2       2               
  Lines         159     138       -21     
==========================================
- Hits           33      10       -23     
- Misses        114     125       +11     
+ Partials       12       3        -9

Impacted Files	Coverage Δ
conform/enforce.go	8.33% <0%> (-15.08%)	:arrow_down:

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[andrewrynhard]

Closes #13.