rgbif v0.9.0

NEW FEATURES

• New set of functions (gbif_oai_*()) for working with
  GBIF registry OAI-PMH service. Now importing oai package to
  make working with GBIF's OAI-PMH service easier (#183)
• Added code of conduct (#180)
• Now sending user-agent header with all requests from this
  package to GBIF's servers indicating what version of rgbif
  and that it's an ropensci package. Looks like
  r-curl/0.9.4 httr/1.0.0 rOpenSci(rgbif/0.9.0), with whatever
  versions of each package you're using. We also pass a user-agent
  string with the header X-USER-AGENT in case the useragent
  header gets stripped somewhere along the line (#185)
• New function gbif_citation() helps get citations for datasets
  eith using the occurrence search API via occ_search() or the
  downloads API via occ_downlad() (#178) (#179)

MINOR IMPROVEMENTS

• Using importFrom instead of import in all cases now.
• Parameter collectorName changed to recordedBy (#184)

BUG FIXES

• Fix to occ_download_meta() print method to handle 1 or more predicate results (#186)
• Fix to occ_issues() to work with return=data and return=all occ_search() output (#188)