fix: semantic and structural error

[aymen94]

Fix Error #92

• add multipart/form-data
• fixdecription to description
• change oneOf to allOf

This is for Google Summer of Code

[cloudify]

thanks @aymen94 , I just gave you write permission on this repo, would you mind re-creating this PR from a branch in this repo (the circleci checks don't run on forks) - thanks

[cloudify]

@ioggstream that's fine with with me, just we can't merge it to master now, I would suggest to create an oas3 branch from the current master and change this PR to be against that branch - once the oas3 branch is stable and complete we can merge it to master.

I suggest to create also a DRAFT PR from oas3 to master to get circleci validate the changes.

[ioggstream]

@cloudify we could

1- split this PR fixing description and multipart: those two should be mergeable
2- leave the rest in the OAS3 fork

Sounds good?

[aymen94]

@cloudify thank for permission.
@ioggstream ok, I make.