The death of the novelist Martin Amis at the age of 73 from esophageal cancer — which also felled his friend, Christopher Hitchens, at 62 in 2011 — marks the passing of an author whose hard work and ample play made him both a celebrity writer and a writer’s writer, equally at ease with tabloids and rough drafts, schooled in the slashing style of literary journalism and accomplished across genres. His work is mixed, but full of moxy.