rnoaa v0.6.6

NEW FEATURES

• isd() now using a new package isdparser to parse
  NOAA ISD files. We still fetch the file within rnoaa, but the
  file parsing is done by isdparser (#176) (#177) (#180) thanks @mrubayet
  for the push

MINOR IMPROVEMENTS

• Fixed precipitation units in docs for meteo_* functions (#178)
  thanks @mrubayet

BUG FIXES

• Fixed bug in ghcnd() where internal unexported function
  was not found (#179)
• Fix to isd_stations() and isd_stations_search() to work
  correctly on Windows (#181) thanks @GuodongZhu
• Changed base URL for all NOAA NCDC functions (those starting with
  ncdc) to https from http (#182) thanks @maspotts
• Changed base URL for all NOAA HOMR functions (those starting with
  homr) to https from http (#183)