File Support

There's no documentation for the digest field in the api schema. Is it md5, sha1, sha256, ...?

Also, I can put anything I want to in this field:

$ cat | http POST :8000/api/v3/content/file/
{
  "digest": "hello world",
  "path": "foo.tar.gz",
  "artifacts": {"foo.tar.gz":"http://localhost:8000/api/v3/artifacts/f05c119f-3ad8-4f96-8dc4-a9264420608e/"}
}
HTTP/1.0 201 Created
Allow: GET, POST, HEAD, OPTIONS
Content-Length: 265
Content-Type: application/json
Date: Sun, 04 Mar 2018 21:55:46 GMT
Location: http://localhost:8000/api/v3/content/file/bb1e4c8b-d2c4-48f1-8682-cf89e5974b06/
Server: WSGIServer/0.2 CPython/3.5.4
Vary: Accept, Cookie
X-Frame-Options: SAMEORIGIN

{
    "_href": "http://localhost:8000/api/v3/content/file/bb1e4c8b-d2c4-48f1-8682-cf89e5974b06/",
    "artifacts": {
        "foo.tar.gz": "http://localhost:8000/api/v3/artifacts/f05c119f-3ad8-4f96-8dc4-a9264420608e/"
    },
    "digest": "hello world",
    "notes": {},
    "path": "foo.tar.gz",
    "type": "file"
}

Better yet, maybe not even have the user specify this field on create? This digest info is available on the artifact.