Please add deepfool/DDN support

[drmeerkat]

Thank you guys for your incredible work ! This toolbox boosts our research a lot.
But we found some more on this topic that DDN and DeepFool are also good attack methods.
Plaease check:
Deep Fool
Decoupling Direction and Norm(NIPS 18' Challenge Top-1)

If possible, I am willing to contribute to this repository and share my implemention of these two methods compatible with your interface later.

[gwding]

@drmeerkat Thanks for bringing this up! For DDN attack, I'll try to work with the authors (or work on it myself) to add it.
For Deep Fool, your contribution is very welcomed!

[drmeerkat]

That's great. Thanks for your quick reply, I'll notify you as soon as I finish Gavin Weiguang Ding <notifications@github.com> 于2019年6月25日周二 下午1:37写道：

…

@drmeerkat <https://github.com/drmeerkat> Thanks for bringing this up! For DDN attack, I'll try to work with the authors (or work on it myself) to add it. For Deep Fool, your contribution is very welcomed! — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#25?email_source=notifications&email_token=AFS6FFPCMHP3X2WI5G7OD4DP4GVLDA5CNFSM4H23OTMKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGODYPCBFA#issuecomment-505290900>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AFS6FFJBTT5USSBAU77FLN3P4GVLDANCNFSM4H23OTMA> .

[jeromerony]

Just made a PR for DDN

[gwding]

@drmeerkat Just to let you know that DDN has been merged to master. #26