Improve `Debug` derive with `[u8]`/`str`

[mcarton]

This:

#[derive(Debug)]
struct Foo {
    data: Vec<u8>,
}

will always print all vector in a very noisy form. Some filters could be nice:

• Print shorter version of the data (remove end/remove middle part): Foo { data: [12, 102, 111, 111, 12, …] } or Foo { data: [12, 102, 111, …, 98, 97, 122] }.
• Print as ascii/UTF-8 when possible: Foo { data: [12, "foo", 12, "bar", 12, "baz"] }.

[auscompgeek]

I would personally like a version where it renders like a bytestring, for example like Foo { data: b"\x01foo bar" }.