Implement the CKAN API

[wouterbeek]

Implement the CKAN API.

This consists of the following tasks:

• Only implement API version 3 (not versions 1 and 2).
• Implement all the functions that are specified for the (not yet released) CKAN version 2.2.
• Also implement the deprecated parameters for all functions (many CKAN sites run CKAN versions 2.0 and 2.1).
• Some functions result in a server error (HTTP status codes 5xx) when called. For this we have to use pagination mode (= requesting the data in chunks called "pages").
• Convert the JSON output to Prolog terms, and then to RDF (using a generic Prolog2RDF converter).
• Use XML Schema 2: Datatypes W3C Recommendation 1.1 for asserting booleans, integers, dates, times, dataTimes, floats, ... (Assert the rest as RDF literals.)

The following sub-APIs will be implemented:

• Action API,
• Datastore API, http://docs.ckan.org/en/latest/datastore.html#the-datastore-api
• Do not implement sub-APIs that are legacy (i.e. pre-2.2) only. E.g. do not implement the Filestore API.

[wouterbeek]

Mostly done now. Adding attributes for CKAN objects as they are needed.