Add a "dump preprocessor output" facility to the CLI

[antecedent]

In #152, the following has been very helpful:

php -r 'require "Patchwork.php"; echo Patchwork\CodeManipulation\transformString(file_get_contents("path/to.php"));' 

It would be nice to turn it into something more convenient, like the following:

php Patchwork.php path/to.php

By the way, Patchwork already has a rudimentary CLI, intended mostly for warming up the preprocessor cache. I think it could be easily remade to also serve this debugging-related purpose.