v2.0.0

• feat(s3)!: stream uploads with upload_fileobj for S3 instead of a single PUT and remove fake checksum returned (#24)
  save() used to read the whole file in memory before a single PUT, so
  an upload was bounded by the RAM of the worker and by the 5GB limit of a
  PUT. It now goes through upload_fileobj, which reads the file by
  blocks and switches to a multipart upload past 8MB.

  It also asks S3 to checksum what it receives, so a corrupted transfer is
  rejected and metadata() still reports a digest of the content whatever
  the number of parts it travelled in. It's a CRC32, the only algorithm S3
  combines over a whole object. checksum is None only for objects
  written before this.

  Checked against the OVH bucket: a 12MB upload comes back with
  ChecksumType: FULL_OBJECT and its CRC32, and a wrong digest is
  rejected with BadDigest.