Merge branch 'cc/interpret-trailers'

A new filter to programatically edit the tail end of the commit log messages. * cc/interpret-trailers: Documentation: add documentation for 'git interpret-trailers' trailer: add tests for commands in config file trailer: execute command from 'trailer.<name>.command' trailer: add tests for "git interpret-trailers" trailer: add interpret-trailers command trailer: put all the processing together and print trailer: parse trailers from file or stdin trailer: process command line trailer arguments trailer: read and process config information trailer: process trailers from input message and arguments trailer: add data structures and basic functions