This commit makes changes to the way variables are referenced:
• Make types Copy when possible
• Make methods take `self` instead of `&self` where possible (trivially_copy_pass_by_ref)
• Remove unnecessary borrowing (needless_ref)
• Remove unnecessary cloning (clone_on_copy)
• Remove `ref` from match arms where possible (new Rust match ergonomics)
This commit uses Clippy to fix all the 'use_self' warnings. Using Self instead of the type name has been good Rust style for a while now, and it's become the style I'm used to seeing.
This commit moves the definitions of Filter and DirAction from the options module to the fs module, but leaves the parts that actually have to do with option parsing alone.
Now, the options module shouldn’t define any types that get used elsewhere in the program: it only adds functionality to types that already exist.
