get_inventory: Download and Return a data.table Object of GSOD Weather Station Data Inventories
Description
The NCEI maintains a document,
https://www1.ncdc.noaa.gov/pub/data/noaa/isd-inventory.txt, which lists
the number of weather observations by station-year-month from the beginning
of the stations' records. This function retrieves that document and prints
an information header displaying the last update time with a data frame of
the inventory information for each station-year-month.