add tests for dot_files to FinderFactoryTest.php
add tests for dot_files to FinderFactoryTest.php

add test_dot_files_are_returned():
full directory content including .dot_file and .dot_dir
add public function test_dot_directory_contents_are_returned():
subdirectory .dot_dir content containing .dot_file
DirectoryLister/DirectoryLister,DirectoryLister/DirectoryLister,DirectoryLister/DirectoryLister,DirectoryLister/DirectoryLister