Add improved 404 page and directory listing pages

.editorconfig

Cargo.lock

Cargo.toml

src/config.rs

src/files/directory/index.rs

src/files/directory/listing.rs

src/files/directory/mod.rs

src/files/error.rs

src/files/mod.rs

src/files/pages.rs

src/files/service.rs

src/lib.rs

src/main.rs

src/not_found.rs

src/server.rs