Consistent roundtrips for whole number floats

[saty9]

When whole numbers other than 0 with decimal places are parsed and then converted back to string they maintain their decimal point unless than number is 0 in which case it gets stripped. it would be useful if 0 also retained its decimal place when being converted back to a string.

    #[test]
    fn test_consistent_output_types() {
        let input = r#"{"one":1.0,"zero":0.0,"one_int":1,"zero_int":0}"#;
        let parsed = json::parse(input).unwrap();
        let output = parsed.to_string();
        
        assert_eq!(input, output);
    }

assertion `left == right` failed
  left: "{\"one\":1.0,\"zero\":0.0,\"one_int\":1,\"zero_int\":0}"
 right: "{\"one\":1.0,\"zero\":0,\"one_int\":1,\"zero_int\":0}"