f16 serialization

[NazarKostetskiy]

Hi. I'm trying to serialize f16, but I'm stuck on it.
I'm using serde feature, but when I use f16_var.serialize(serializer) I'm getting unexpected results.

Example:
Value: 1.0
Serialization result: "15360"`

If I convert the value to f32 and serialize it, everything is fine, I will get "1.0"` as expected.

Running on Ubuntu 20 under WSL

[starkat99]

Currently f16 is being serialized as a u16, which works for binary formats, but not so much for string serialization. Will just need to do custom serialization implementation rather then using derive.

[gauteh]

Same issue in JSON:

        let f = half::f16::from_f32(45.0);
        println!("{}", json::to_string(&f).unwrap());

20896

[starkat99]

Added serde adapters to support this, since serde has design limitations preventing different serialization for different output formats. Use #[serde(serialize_with="f16::serialize_as_f32")] in derive macros of types containing f16 to see float values in JSON or other string output formats.