ManifestoAvailability objects are data.frames with variables party
and date identifying the requested manifestos as in the Manifesto
Project's Main & South America Datasets. The additional variables
specify whether a machine readable document is available (manifestos),
whether digital CMP coding annotations are available (annotations) or
whether an orignal PDF is available (originals).
Additional a ManifestoAvailability object has attributes query, containing
the original id set which was queried, corpus_version, specifying the
Corpus version ID used for the query, and date with the timestamp of the query.