Add a state machine library

[codecov[bot]]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (f99d254) 81.17% compared to head (6134a79) 81.16%. Report is 1 commits behind head on master.

Files	Patch %	Lines
src/lib/sm.c	53.33%	0 Missing and 14 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #597 +/- ## ========================================== - Coverage 81.17% 81.16% -0.02% ========================================== Files 187 189 +2 Lines 26683 26742 +59 Branches 4865 4859 -6 ========================================== + Hits 21661 21704 +43 + Misses 3478 3455 -23 - Partials 1544 1583 +39 ```

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