Writer object should be reusable and do validation by assertion

[miloyip]

Writer should always produce well-formed JSON. Invalid sequence of events should be detected via assertion. However, currently generating two or more JSONs into output stream does not generate assertion fail. For example,

Writer<Stream> writer(stream);
writer.StartObject();
writer.EndObject();
writer.StartObject();
writer.EndObject();

Will output {}{} to the stream.

I suggest that an explicitly reset API should be added:

Writer<Stream> writer(stream);
writer.StartObject();
writer.EndObject();
writer.Reset(newStream);
writer.StartObject();
writer.EndObject();

So that, error of multiple root elements can be detected, and also Writer object can be reused. The advantage of reusing an Writer object is to prevent reallocating memory for Writer's internal data structure (basically a stack).

[miloyip]

Writer::Double() should detect NaN and +/-inf as well (via assert). These are not valid JSON number in the standard.

[miloyip]

There is a locale issue in up-stream as well. https://code.google.com/p/rapidjson/issues/detail?id=84