v0.5.2

NEW FEATURES

• New data source added: ARGO buoy data. See functions starting with argo() (#123)
  for more, see http://www.argo.ucsd.edu/
• New data source added: CO-OPS tide and current data. See function coops_search()
  (#111) for idea from @fmichonneau (#124) for implementing @jsta See http://co-ops.nos.noaa.gov/api/
  also (#126) (#128)

MINOR IMPROVEMENTS

• rgdal moved to Suggests to make usage easier (#125)
• Changes to ncdc_plot() - made default brakes to just default to what
  ggplot2 does, but you can still pass in your own breaks (#131)