rnoaa v0.6.0

NEW FEATURES

• A large PR was merged with a suite of functions. Most functions added
  a prefixed with meteo_*, and are meant to find weather monitors near
  locations (meteo_nearby_stations), find all monitors within a radius
  of a location (meteo_distance), calculate the distances between a
  location and all available stations (meteo_process_geographic_data),
  calculate the distance between two locations (meteo_spherical_distance),
  pull GHCND weather data for multiple weather monitors (meteo_pull_monitors),
  create a tidy GHCND dataset from a single monitor (meteo_tidy_ghcnd),
  and determine the "coverage" for a station data frame (meteo_coverage()).
  In addition, vis_miss() added to visualize missingness in a data.frame. See
  the PR diff against master
  for all the changes. (#159) Thanks a ton to @geanders et al. (@hrbrmstr,
  @masalmon, @jdunic, @njtierney, @leighseverson, @RyanGan, @mandilin, @jferreri,
  @cpatrizio88, @Ryan-Hicks, @Ewen2015, @mgutilla, @hakessler, @rodlammers)

MINOR IMPROVEMENTS

• isd_stations_search() changed internal structure. We replaced
  usage of geojsonio and lawn for faster dplyr::filter for
  bbox inputs, and meteo_distance() for lat/long/radius inputs
  . This speeds up this function significantly. Thanks to @lukas-rokka
  (#157)
• isd_stations_search() and isd_stations() now return
  tibble's instead of data.frame's
• Removed cached ISD stations dataset within package to reduce
  package size. Only change is now that on first use of the function
  the user has to download the entire thing, but on subsquent
  uses it will pull from the cached version on the users machine.
  isd_stations_search() now caches using rappdirs (#161)
• Convert all is() uses to inherits()

BUG FIXES

• Fixed seaiceeurls() function that's used to generate urls for
  the seaice() function - due to change in NOAA urls (#160)
• Fix to function ghncd_split_vars() to not fail on dplyr::contains
  call (#156) thanks @lawinslow !