Use path-based control-flow analysis

[timholy]

This uses a more sophisticated approach to analyzing control flow,
asking which paths include execution of the required statements and
ensuring we mark those statements that affect critical branching.

Fixes #87

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (b576f6a) 94.50% compared to head (778fe46) 94.51%.
Report is 4 commits behind head on master.

Files	Patch %	Lines
src/codeedges.jl	96.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #88      +/-   ##
==========================================
+ Coverage   94.50%   94.51%   +0.01%     
==========================================
  Files           5        5              
  Lines        1146     1185      +39     
==========================================
+ Hits         1083     1120      +37     
- Misses         63       65       +2     

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[timholy]

There are failured on nightly, but those can be investigated later.