feat: add --unified flag

[raylu]

this actually adds 3 flags:

--help
--unified, -u
--debug

we can add support for a config file via https://cli.urfave.org/v3/examples/flags/value-sources/#values-from-alternate-input-sources-yaml-toml-and-others

closes #10

[zDonik1]

I believe we should instead have a --side-by-side, -s flag just like how delta does it. It doesn't make sense to enforce non-default behavior of delta and make it the default.