Log Message:
(geography/R-countrycode) Updated 1.4.0 to 1.6.0

## countrycode 1.6.0

* Important speed-up for detection of country names using regular expressions \ 
(Thanks to Etienne Bacher).
* `countryname` gets the `nomatch` argument.
* `countryname` returns NA when the code does not support a given country. \ 
(Issue #336)
* Improved regex for Italy
* `eurocontrol_statfor` updated: ESRA->ECAC to account for
  redistribution:
  https://www.eurocontrol.int/sites/default/files/2020-11/eurocontrol-forecast-2020-
  2024-region-definition.pdf Thanks to @sthonnard for contribution #352.
* Antarctica now has a "continent" value. Thanks to @geryan for report \ 
#353.

## countrycode 1.5.0

* `get_dictionary()` function to download custom dictionaries (cross-walks):
  - US States, Swiss Cantons, Global Burden of Disease, ExioBase, GTAP.
* New codes: Polity V "p5c", "p5n"
* New code "unhcr_region". Thanks to @galalH for code contribution #329
* Many regex improvements
* Several minor bug fixes