Mark GET /documents/upload and GET /documents/{id}/upload as deprecated, and add POST /documents/{id}/versions/upload

[reganwolfrom]

Now with checksums being an option, GET /documents/upload and GET /documents/{id}/upload should be deprecated in favour of the existing POST /documents/upload and a new version-specific POST endpoint for a new version.

[reganwolfrom]

We're not going to deprecate this; we will revisit in 2.*