IndEcol/country_converter: ioc and continent classification

<h2>1.2 - 20231212</h2> <h3>Classifications</h3> <ul> <li>added IOC classification (by @Azrael3000)</li> <li>added 7 continents classification (by @marthhoi)</li> <li>assigned Heard Island and McDonald Islands to Antarctica</li> </ul&gt