Print the contents of the expected token when a serialize assert fails

[Marwes]

Before

expected Token::Str but serialized as Str(“F9168C5E-CEB2-4FAA-B6BF-329BF39FA1E4")

After

expected Token::Str(“f9168c5e-ceb2-4faa-b6bf-329bf39fa1e4”) but serialized as Str(“F9168C5E-CEB2-4FAA-B6BF-329BF39FA1E4")

[Marwes]

serde_test/src/de.rs handles this is a much simpler way but unfortunately I get lifetime errors from some uses when I tried it so instead I needed to do this.

[dtolnay]

Thanks! It would be good to clean up ser.rs when one of us gets the chance. A lot of this code is from literally the day before the 1.0 release when the focus was only on API and sometimes the implementation turned out sloppy.