message: Avoid necessitating a vector allocation when parsing ascii samples
diff: use std::io::{self, BufRead, BufReader, Read};
  -use std::str::FromStr;
  +use std::str::{self, FromStr};
  use std::fmt::Display;
  use super::{ArbitraryHeader, ArbitraryTuplType, BitmapHeader, GraymapHeader, PixmapHeader};
  @@ -513,7 +513,7 @@ fn read_separated_ascii<T: FromStr>(reader: &mut Read) -> ImageResult<T>
  ));
  }
  - let string = String::from_utf8(token)
  + let string = str::from_utf8(&token)
  // We checked the precondition ourselves a few lines before, `token.is_ascii()`.
  .unwrap_or_else(|_| unreachable!("Only ascii characters should be decoded"));
  