v3.1.0

Adds income for the employed: a gross annual income in the country's currency (core::money), from ILOSTAT earnings by country, sex, occupation group, age and education, with pay within a group from four national surveys. 199 countries. Every other field is the same as 3.0.3's for the same seed; the JSON gains "income" and the data hash changes, so known answers do. About 0.2 us more per call.