Merge pull request #96 from wardi/master

README: new schema_description description; renamed dataset_fields_by_ckan_id and resource_fields_by_ckan_id
proposed_schema: add ckan type, fix language example
metadata schema: convert gc_multiplicity to mandatory T/F
metadata schema: include types for all fields from proposed_schema
metadata schema: remove unused proposed_name, proposed_type fields
README: list new field types
fix field description links