TSimpleJsonProtocol serialization on string with inner quotes does not produce valid JSON.

There is an issue in the generation of JSON from the TSimpleJSONProtocol, where if there are quotes inside of a string, then those quotes will not be serialized correctly. These quotes need one more layer of escaping to produce valid JSON.

For instance, if you have the Thrift structure defined by:

struct MyThriftStruct {
    1: required string my_string
}

And, I then define an object of that type in Java:

MyThriftStruct t = new MyThriftStruct();
t.my_string = "I said: \"this is a fairly nice string.\""

And, if I then serialize this using the TSimpleJsonProtocol in this manner:

TSerializer thriftJsonSer = new TSerializer(new TSimpleJSONProtocol.Factory());
String myThriftStructJsonString = return thriftJsonSer.toString(t);

This will result in JSON that cannot be deserialized because the quotes inside of the string were not escaped properly.