Yarraman

Bug fixes

• Fixes a bug with links to documentation from get_historical() and %>%

• Updates station location databases to use updated BOM URLs, thanks to @ozjimbob for reporting

• Updates file and error handling for image downloads when downloads fail

• Ensures that .Rds/.Rda files are saved using version 2, for R from 1.4.0 to
  3.5.0 such that users using older versions of R do not have to upgrade to use
  bomrang

• Fixes bug that prevents end-user from self-updating internal databases

Minor changes

• Plots radar images natively using re-exported raster::plot()

• Adds sweep_for_forecast_towns(), which works analogously to
  sweep_for_stations(), thanks to @Rensa for adding