Code review: JSON unmarshaller

[Tyler Jameson Little]

I could make my marshaller/unmarshaller only update objects in 
place. I think this is more useful and would remove the overlap 
between orange and the JSON library. We could then write a JSON 
archiver for orange and include it in std.json as well.

The call to unmarshal would look like:

bool unmarshalJSON(T)(JSONValue val, out T ret);

The following restrictions would apply:

* T must be fully instantiated (all pointers are valid [not null])
* T must not be recursive (results in infinite recursion, and 
hence stack overflow)

And the marshaller:

JSONValue marshalJSON(T)(in T val);

For marshalling, the restrictions are:

* Slices are handled as if they were an array (copy all values)
* Same as unmarshaller, except null pointers will be treated as 
JSON null

I really like Go's JSON marshaller/unmarshaller, so I'm trying to 
model after that one. It allows updating an object in place, 
which was already a goal.

There should probably be some standard D serialization format. In 
working with a structure trained on data (for machine learning, 
natural language processing, etc), a complete serialization 
solution makes sense. But for simple data passing, JSON makes a 
lot of sense.

What do you think, do you think there's a place in Phobos for a 
simple JSON marshaller/unmarshaller?

I'll have some updated code soon, and I'll post back when that's 
done, in case you'd like to have a look.