feat: Add .todosignore file support.

[ianlewis]

Fixes #125

Adds support for a .todosignore file that works exactly the same way as the .gitignore and uses the same format.

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 78.44%. Comparing base (aeec9ab) to head (ef50131).
Report is 237 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/walker/walker.go	72.72%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #135      +/-   ##
==========================================
- Coverage   78.50%   78.44%   -0.07%     
==========================================
  Files          15       15              
  Lines         977      988      +11     
==========================================
+ Hits          767      775       +8     
- Misses        151      153       +2     
- Partials       59       60       +1     

Files with missing lines	Coverage Δ
internal/walker/walker.go	58.78% <72.72%> (+0.99%)	⬆️

[ianlewis]

Windows tests are currently being held up by ianlewis/go-gitignore#3 because go-gitignore keeps the file handles open.

[ianlewis]

Need to use https://github.com/ianlewis/go-gitignore after ianlewis/go-gitignore#16 gets merged.

[ianlewis]

Now we need to wait for these bugs to get fixed so that it works on Windows.

• MatchAbsolute fails on Windows go-gitignore#17
• TestNew* fails on Windows go-gitignore#18
• TestInvalidRepository fails on Windows go-gitignore#19

[github-actions]

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