ripc 0.2.1

• Improved ipc_get_population() to deal with missing areas data when it is
  removed from the API.
• Fixed assert_start_end() so it correctly tests start and end parameters
  without generating an error.
• Fixed ipc_get() to initially read all numeric vectors as character in as
  some errors were created in nested data frames that only contained integers.
• Ensured that all ipg_get_...() functions returned properly parsed numeric
  columns and fixed some unnesting data frames in ipc_get_areas().