citecorp v0.2.0

NEW FEATURES

• the functions oc_doi2ids, oc_pmid2ids, and oc_pmcid2ids (see ?oc_lookup) now all accept more than 1 identifier. the underlying SPARQL queries were modified to make this possible. (#1)
• three new package datasets (oc_dois, oc_pmids, oc_pmcids) with vectors of identifiers of each of those types for testing and examples

BUG FIXES

• fixed an error in parsing results in oc_lookup functions - this fix was later changed as part of another fix, but still appreciated (#2) (#3) thanks @Selbosh
• fix to parsing in oc_lookup functions: only retrieve data.frame columns if they exist - prevents error on retrieving a column that doesn't exist (#4) thanks @Selbosh