Refactor add_package.rs

[Kixiron]

• Made the function signatures readable (Still need further work with splitting into separate functions)
• Changed passing integers by reference into passing them directly, pointers are larger than i32s
• Overall style and formatting changes

[jyn514]

As discussed on discord, I think having one principled rustfmt PR would be better than formatting piecemeal and mixing it with other clippy lints/style issues. I'm happy to take this change:

Changed passing integers by reference into passing them directly, pointers are larger than i32s

but I think the rest are not the best direction for docs.rs at this time.