This option wasn't converted to a proper data type when it was renamed from "week_begins_on_monday" to "general.firstdayofweek". Convert the boolean option into an enumeration type that can take the values "monday" and "sunday". Also, update the documentation, add a conversion rule to the upgrade script and convert the configuration file used in the test suite. Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>