Writes the panel and, by default, its codebook next to it
(<name>_codebook.csv). Stata files carry variable labels from the
codebook.
Examples
p <- build_panel(states = "CA", years = 2010:2020, groups = "rps",
rps_methods = "nominal")
f <- tempfile(fileext = ".csv")
export_panel(p, f)
head(read.csv(f))
#> state state_name fips year rps_nominal
#> 1 CA California 6 2010 0.2000000
#> 2 CA California 6 2011 0.2000000
#> 3 CA California 6 2012 0.2000000
#> 4 CA California 6 2013 0.2000000
#> 5 CA California 6 2014 0.2166667
#> 6 CA California 6 2015 0.2333333