Interview problem implementation

The approach I took was basically to assume the existing file is correct, in general, but especially if the value for a given key in the original file (if provided) matches the new file. In that case, the local value is just taken--likewise if the local value matches the new value for the key. In cases where they don't match, and there is no original file or the key doesn't exist in the original file, the local value is merged in, but the key is added to a dict of 'questionable' keys. At the end of merging, if there are any such questionable keys, the user is implored to examine and manually correct them.

I also have a few notes at the end of the script that outline how I'd go about redoing it to support preserving comments. It seems doable to me, but probably would take more than a couple of hours.

cc @mbulman -- please feel free to cc any other team members who might want to see/review