Topic/remove munger

I noticed, while debugging a plugin bundle with  Dist::Zilla::App::Command::dumpphases, that this plugin added a file in the FileGatherer phase and then munged it in the FileMunger phase.  This patch switches to doing all the work in FileGatherer, by modifying the file as it is created.

(I also added use strict; use warnings; and a Test::More version to the test that is generated.)

thanks for this plugin; I use it every day! :)