Support simple object serialization

[petermoore14]

The MemoryHandler allows one to use joi.objects as attributes, for example:

position: jsonApi.Joi.object({
  x: jsonApi.Joi.number().required(),
  y: jsonApi.Joi.number().required()
}).required(),

Unfortunately, this explodes when using relationaldb (tested with postgres), which reflects the fact that the 'object' type doesn't seem to be properly handled. Ideally relationaldb would be able to handle simple objects like this in situations where relationals like one, many, ... aren't appropriate or would be overkill.