handle most blob and storages actions:

* blobs actions

- GET /<storage> : list blobs in the storage, limit as optional
  parameter
- POST /<storage> MULTIPART BODY : upload multiple blobs
- HEAD /<storage>/<blobref> : return 200 if the blob exists, 404 not
  found
- GET /<storage>/<blobref> : stream the blob to the client
- PUT /<storage>/<blobref> : upload a blob
- DELETE /<storage>/<blobref> : delete a blob

* storages

GET /storages : list all storages available