Better support for deserializing enum variants

[spyoungtech]

right now, this fails:

        use serde::Deserialize;
        use crate::from_str;
        #[derive(Debug, Clone, Deserialize, Serialize, PartialEq)]
        #[serde(rename_all="snake_case")]
        enum SomeEnum{
            VariantA(String),
            VariantB,
        }

        #[derive(Debug, Clone, Deserialize, Serialize)]
        struct SomeStruct {
            some_enum: SomeEnum
        }


        let json5 = r#"{some_enum: "variant_b" }"#;
        let parsed: SomeStruct = from_str(json5).unwrap();
        assert_eq!(parsed.some_enum, SomeEnum::VariantB);

This should work as it does in serde_json

Right now, we only consider Identifiers and JSONObjects (and only identifiers within JSONObjects) this should at least also consider strings, too.