Marshall Hall: A Law unto Himself by Sally Smith Wildy, Simmonds & Hill, 2016, 302 pages, £25 _____________________________________   The best-known trial lawyers of the post-war era are fictional characters. They either originated on the big screen or got there eventually. They include Gregory Peck’s Atticus Finch, Paul Newman’s Frank Galvin and Richard Gere’s Martin Vail. But in much earlier days, the celebrity barristers were real men. Sir Edward Marshall Hall KC (1858–1927) combined elements of all these later heroes of American drama: Finch’s passion, Galvin’s desperation and Vail’s conviction, almost embarrassed and hidden beneath the infuriating coolness of the…