Most of the fields are already implemented for cards/put with exception of:
* openlist (actually quite simple, just reuse getFieldsData already used for CSV import, SOAP and XML import)
* permissions on artifacts
* attachements/files (not covered by this story)

/v1/artifacts
POST <= {Artifact_Info} for artifact creation. "id" is not submitted of course, the ID of the created artifact is returned in the response.

Note:
The tracker ID is passed in the JSON object :
{..., "tracker":{"id": 123}, ...}
to be consistent with the input format of artifacts and other JSON objects that reference a tracker.

/v1/artifacts/:id
PUT <= {Artifact_Info_With_Comment} - Updates given fields,
non-given fields are not modified,
field given with value null are set to null,
unknown fields are ignored,
Artifact_Info can include a comment field.

Note:
We haven't planned any particular route for adding comments to an artifact, for us it's supposed to be the /artifacts/:id route that allows that. The reason is simple: we want to be able to submit at the same time the changes to apply to an artifact and the related comment, so there must be one route for this.
Nevertheless, comments retrieval is made thanks to already existing routes (that we haven't tested yet):
/artifacts/:id/changesets => { id, message, format }
/artifacts/:id/changesets?_fields=all => { id, message, format, fields }