states 0.3.0

Although the original COW state list does not distinguish micro-states, like the G&W list does, the cowstates data now has a microstates coding derived from the G&W coding (#24). This makes it easier, for example, to filter out micro-states from a state panel dataset.
In the gwstates and cowstates data, the "iso3c" columns have been renamed to "gwn" and "cown", as they are not in fact ISO 3-character country abbreviations (#19).
plot_missing()'s "space" argument has been renamed "ccode".
id_date_sequence() now works with integer years, there is no need to convert them to Date class anymore (#20).

Improved support for state_panel shortcuts

state_panel() has further improved support for input shortcuts (#3):

Accepted formats for the "start" and "end" arguments now include 2006, "2006", "2000-06", and "2006-06-01". See parse_date() for details.
The implied time period is now also inferred from shortcut input when "by" is left at the new default of NULL.
The "partial" option has gained new "first" and "last" values that also support shortcut input. Previously a shortcut input like 2006 could only be used with the "any" partial option, and to get country-years for states that were independent on the first day of a year one had to use state_panel("YYYY-01-01", partial = "exact", ...). This can now instead be done with state_panel(2006, partial = "first", ...).

Added country_names() to translate country codes to country names and prettyc() to shorten some of the longer country names, like "Macedonia, the former Yugoslav Republic of".
Updated vignette on G&W and COW differences to take into account when trying to translate between codes.
Added compare() helper to compare two statelist data frames prior to merging.
Added parse_date() to handle more flexible "start" and "end" date input (#12).

all.equal() in R 4.1.x (R-devel at this point) will check environments for equivalence as well. This breaks one test since 2e testthat relies on all.equal() for expect_equal(). (#26)
fixed a misspelled country name, "Rumania" to "Romania"