Fix code style issues
Fix compile warning: use of deprecated item

Full warning:
warning: use of deprecated item: use `Show` (`{}` format specifier),
cut.rs:444             show_error!("Invalid options\n{}", f.to_err_msg())
Fix warnings and simplify list_to_ranges()
Fix compiler unused result warnings

Add .unwrap() to all .write() calls. Does incur a very slight decrease
in performance.