Configure the search behaviour with a file like `shisho.yaml`

[lmt-swallow]

Problem

We added --exclude flag as a workaround for #94. However, this approach needs users to add --exclude flag every time they run Shisho.

Possible Solutions

We can (1) use .gitignore-like configuration files to determine paths to ignore (as Semgrep does), or (2) use another YAML file that includes configurations not only on file exclusion but also on the behaviour of Shisho.

Additional Notes

See https://github.com/flatt-security/shisho/issues/94#issuecomment-932592022 and https://github.com/flatt-security/shisho/issues/94#issuecomment-932696749. @ihrwein -san, thank you for your proposal!