[FEATURE] For duplicates add: 2, 3, 4 etc.. to the end of the filename

[mattjis]

• Verified and I assure that I'm running youtube-dl 2017.04.26
• At least skimmed through README and most notably FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones

Purpose of this issue?

• Feature request (request for a new functionality)

Description:

For playlists there is currently no way to keep the filenames perfectly organized. I want the filename to be the exact title + extension. At the moment the best I can do is: %(playlist_index)s. %(title)s.%(ext)s.

I'd really love to be able to just use %(title)s.%(ext)s and for youtube-dl to allow duplicates just by adding X to the end of the filename.

Maybe something like: --number-duplicates

Example:

CURRENT NAMING:
01. title.mp3
02. titlehere.mp3
03. titlehere.mp3

WITH THIS FEATURE:
title.mp3
titlehere.mp3
titlehere 2.mp3