Account for ! and ? and add tests

[cparros]

PR Checklist

• Addresses an existing open issue: fixes Does not detect sentences ending with ! or ? #22
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken
  x

Overview

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (6888be1) 86.36% compared to head (607e9c3) 75.37%.
Report is 23 commits behind head on main.

Files	Patch %	Lines
src/sentences-per-line.ts	33.33%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #114       +/-   ##
===========================================
- Coverage   86.36%   75.37%   -11.00%     
===========================================
  Files           2        2               
  Lines         132      134        +2     
  Branches       25       25               
===========================================
- Hits          114      101       -13     
- Misses         18       33       +15     

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