[C++] Generate message pretty printers

[agmt]

To solve issue: #178
For GeneratedStubExample it generates json-like string: {"Name": "Car", "sbeTemplateId": 1, "serialNumber": 1234, "modelYear": 2013, "available": "T", "code": "A", "someNumbers": [0,1,2,3], "vehicleCode": "abcdef", "extras": ["sportsPack","cruiseControl"], "discountedModel": "C", "engine": {"capacity": 2000, "numCylinders": 4, "manufacturerCode": "123", "efficiency": 0, "boosterEnabled": "F", "booster": {"BoostType": "NITROUS", "horsePower": 200}}, "fuelFigures": [{"speed": 30, "mpg": 35.9, "usageDescription": "Urban Cycle"}, {"speed": 55, "mpg": 49, "usageDescription": "Combined Cycle"}, {"speed": 75, "mpg": 40, "usageDescription": "Highway Cycle"}], "performanceFigures": [{"octaneRating": 95, "acceleration": [{"mph": 30, "seconds": 4}, {"mph": 60, "seconds": 7.5}, {"mph": 100, "seconds": 12.2}]}, {"octaneRating": 99, "acceleration": [{"mph": 30, "seconds": 3.8}, {"mph": 60, "seconds": 7.1}, {"mph": 100, "seconds": 11.8}]}], "manufacturer": "Honda", "model": "Civic VTi", "activationCode": "deadbeef"}