implement UnmarshalJSON interface

[levinalex]

This patch makes it possible to deserialize JSON into jason.Values directly. This is useful if jason.Values are used as part of a larger struct like so:

type X struct {
  key string `json:"key"`
  value jason.Value `json:"value"`
}

var x X

str := `{"key": "foo", "value": { "a": 3, "b": "bar" }}`
json.Unmarshal([]byte(str), &x)

For this to be useful I had to move Implementations of the Get...set of methods from Object over to Value, I'm not sure this is correct and a good Idea. I don't really understand why the Value/Object distinction exists.

[tgccc]

iosjason