Formatting and shortening byte slices as hexadecimal strings

This crate provides wrappers for byte slices and lists of byte slices that implement the standard formatting traits and print the bytes as a hexadecimal string, eliding from the middle if the length would exceed the precision format parameter.

```rust use hex_fmt::{HexFmt, HexList};

asserteq!("090a0b", &format!("{}", HexFmt(&[9u8, 10, 11]))); let ninetof = [9u8, 10, 11, 12, 13, 14, 15]; asserteq!("090..0f", &format!("{:.7}", HexFmt(&ninetof))); asserteq!("090..e0f", &format!("{:.8}", HexFmt(&ninetof))); asserteq!("090a..0e0f", &format!("{}", HexFmt(&ninetof))); assert_eq!("[4142, 4241]", &format!("{}", HexList(&[b"AB", b"BA"]))); ```