Electronic books, having changed the way many people read for pleasure, are now seeping into schools, the Washington Post reports. Starting this fall, almost all Fairfax middle and high school students began using online books in social studies, jettisoning the tomes that have weighed down backpacks for decades. It is the Washington area’s most extensive foray into online textbooks, putting Fairfax at the leading edge of a digital movement that publishers and educators say inevitably will sweep schools nationwide…