REYKJAVIK, Iceland — Iceland has elected a female-majority parliament, a landmark for gender equality in the North Atlantic island nation, in a vote that saw centrist parties make the biggest gains. After all votes were counted Sunday, female candidates held 33 seats in Iceland’s 63-seat parliament, the Althing. The three parties in the outgoing coalition government led by Prime Minister Katrin Jakobsdottir won a total of 37 seats in Saturday’s vote, two more than in the last election, and appeared likely to continue in power. The election makes Iceland the only country in Europe, and one of a handful in the world, with a majority of female lawmakers.