Upload a download artifact

Upload new download artifacts.

To upload files, perform a multipart/form-data POST containing one or more files fields:

$ echo Hello World > hello.txt
$ curl -s -u evzijst -X POST https://api.bitbucket.org/2.0/repositories/evzijst/git-tests/downloads -F files=@hello.txt

When a file is uploaded with the same name as an existing artifact, then the existing file will be replaced.