pangaear v0.2.4

MINOR IMPROVEMENTS

• Improved examples in the OAI methods to make sure they work
  regardless of when the user runs them

BUG FIXES

• Fixes to pg_search() needed due to changes in the Pangaea
  website. Nearly identical functionality, but one parameter switch
  (env param is now topic). More parameters may be added in the
  future. New fields are added to output, added to docs for the
  function. Now importing jsonlite as a result of these changes (#50)
• Fixes to pg_data() needed due to changes in the Pangaea
  website. Nothing should be different for the user. (#51)