Support gitignore

[theopomies]

Adds support for filtering out gitignored files

This feature adds a --gitignore CLI flag and a gitignore (optional) boolean key in the config file for filtering out gitignored files.

It makes use of the GitStatus and GitCache structures to provide this feature.

I wrote tests for the Config and Cli flag but couldn't figure out how to write integration tests, I didn't find any tests for the GitStatus or IgnoreGlobs features to take inspiration from.

This partially solves #218 and #342

TODO

• Use cargo fmt
• Add necessary tests
• Update default config/theme in README (if applicable)
• Update man page at lsd/doc/lsd.md (if applicable)

[muniu-bot]

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