Changed variable names and tweaked output
Removed '-ok' safety argument
Implemented searching for file sizes before checking real content

Duplicate files share the same size, so it is a bit more memory-efficient
to check for the file sizes first and only read contents of those files
which share the same size.

This way, the software won't overflow in memory due to reading files which
are only present once.
Added option for dry-running
Modified list possible duplicates: now ordered by file size, descending