Igniter.delete_file/2

[ibarakaiev]

Igniter currently lacks functionality to stage files for deletion. Note that Rewrite.delete/2 and Rewrite.drop/2 both remove the file from the list of sources but leave the actual files unaffected, whereas Rewrite.rm/2 deletes the file right away. So we need a custom way to track what files are about to be deleted, keeping in mind file moves, future possible re-adding files back, etc.

[ibarakaiev]

Note: if a file is deleted and its directory became empty, the directory should also probably be deleted (all the way up, until lib or test). Same should actually probably happen in igniter.move_files.