Support multi-file patches like git-format-patch features

[weihanglo]

Hi! Thanks for diffy. It works great for single-file unified diffs.

I'm interested in extending diff parsing to support:

• Multiple files in a single patch (like git diff output)
• git-format-patch features (binary patches, file renames/copies)

This is motivated by

• Allow patching dependencies with patch files rust-lang/cargo#4648
• Allow registries to patch crates rust-lang/cargo#14458

Though I am not sure if this is something you'd like to add to diffy, or be opened to pull requests for those.

I understand if this is out of scope for the project. Just wanted to ask before going a separate direction. Thank you!