custom derserialize for support u8 and seq directly

[zwpaper]

Hi,

I have created a custom deserializer for Colour, after using the custom one, we can deserialize like below:

{"colour": "Red"}

{"colour": 255}

{
  "colour": {
    "Fixed": 255
  }
}

{"colour": [255,255,255]}

{
  "colour": {
    "Red": [255,255,255]
  }
}

this keeps the compatibility and provided a more convenient way to deserialize Colour

[zwpaper]

looks like channel 1.28.0 can not cowork with serde_json v1.0.61?

copied logs from AppVeyor:

Downloading serde_json v1.0.61
error: unable to get packages from source

Caused by:
  failed to parse manifest at `C:\Users\appveyor\.cargo\registry\src\github.aaakk.us.kg-1ecc6299db9ec823\serde_json-1.0.61\Cargo.toml`
Caused by:
  editions are unstable
Caused by:
  feature `edition` is required
this Cargo does not support nightly features, but if you
switch to nightly channel you can add
`cargo-features = ["edition"]` to enable this feature

[zwpaper]

hi @ogham ci passed, could you spend some time to review this PR?