Add micro states coding for COW state list

[andybega]

Currently the "microstate" TRUE/FALSE that the GW states list has is not present in the COW list, since the original COW state list does not code this. Adapt the GW coding for the COW state list so these are not missing anymore.

library(states)
data(gwstates)
head(gwstates)
#>   gwcode gwc             country_name      start        end microstate
#> 1      2 USA United States of America 1816-01-01 9999-12-31      FALSE
#> 2     20 CAN                   Canada 1867-07-01 9999-12-31      FALSE
#> 3     31 BHM                  Bahamas 1973-07-10 9999-12-31      FALSE
#> 4     40 CUB                     Cuba 1902-05-20 9999-12-31      FALSE
#> 5     41 HAI                    Haiti 1816-01-01 1915-07-04      FALSE
#> 6     41 HAI                    Haiti 1934-08-15 9999-12-31      FALSE
data(cowstates)
head(cowstates)     
#>   cowcode cowc             country_name      start        end
#> 1       2  USA United States of America 1816-01-01 9999-12-31
#> 2      20  CAN                   Canada 1920-01-10 9999-12-31
#> 3      31  BHM                  Bahamas 1973-07-10 9999-12-31
#> 4      40  CUB                     Cuba 1902-05-20 1906-09-25
#> 5      40  CUB                     Cuba 1909-01-23 9999-12-31
#> 6      41  HAI                    Haiti 1859-01-01 1915-07-28

# shows up as missing when using sfind()
sfind(20)
#>     list ccode code3c country_name      start        end microstate
#> 2     GW    20    CAN       Canada 1867-07-01 9999-12-31      FALSE
#> 241  COW    20    CAN       Canada 1920-01-10 9999-12-31         NA

^{Created on 2020-10-23 by the reprex package (v0.3.0)}

[andybega]

Wups, duplicate of https://github.com/andybega/states/issues/21