Filtering

Similar issue to sort [camp-187]. GUI clients woudl typically expect to be able to issue API requests to filter the List resources by attributes of the entities referred to in the Links, including (but not restricted to) the name. Typical syntax is of the form ?attr=value or ?attr=val* Again there is no obvious convention to follow

Need to understant how to avoid conflict with the select_attr query parameter in the (slightly obscure) case where an attribute in an extension happens to be called "select_attr", which is allowed by the spec.