- plugin XEP-0447 can now be used in message attachments and to retrieve an attachment
- plugin attach: `attachment` being processed is added to `extra` so the handler can inspect it
- plugin attach: `size` is added to attachment
- plugin download: a whole attachment dict is now used in `download` and
`file_download`/`file_download_complete`. `download_uri` can be used as a shortcut when
just a URI is used. In addition to URI scheme handler, whole attachment handlers can now
be registered with `register_download_handler`
- plugin XEP-0363: `file_http_upload` `XEP-0363_upload_size` triggers have been renamed to
`XEP-0363_upload_pre_slot` and is now using a dict with arguments, allowing for the size
but also the filename to be modified, which is necessary for encryption (filename may
be hidden from URL this way).
- plugin XEP-0446: fix wrong element name
- plugin XEP-0447: source handler can now be registered (`url-data` is registered by
default)
- plugin XEP-0447: source parsing has been put in a separated `parse_sources_elt` method,
as it may be useful to do it independently (notably with XEP-0448)
- plugin XEP-0447: parse received message and complete attachments when suitable
- plugin XEP-0447: can now be used with message attachments
- plugin XEP-0447: can now be used with attachments download
- renamed `options` arguments to `extra` for consistency
- some style change (progressive move from legacy camelCase to PEP8 snake_case)
- some typing
rel 379
