rredlist v0.4.0

NEW FEATURES

• Gains new functions rl_growth_forms() and rl_growth_forms_(). added
  tests for them as well (#20) thanks @stevenpbachman

MINOR IMPROVEMENTS

• Now using markdown documentation (#22)
• Fixed many man files which for region parameter described
  requiring a taxonomic name - fixed to describe accurately. Also
  improved docs in general (#21)
• Added the options for category parameter in rl_sp_category() function
• Added in docs for rl_sp_country how to get acceptable country codes to
  pass to country parameter
• Added to package level manual file ?rredlist-package a note from the
  IUCN Redlist API documentation about that they suggest using taxonomic
  names instead of IDs because IDs can change through time