azurefiles: finish docs and implementation and add optional interfaces

- use rclone's http Transport
- fix handling of 0 length files
- combine into one file and remove uneeded abstraction
- make `chunk_size` and `upload_concurrency` settable
- make auth the same as azureblob
- set the Features correctly
- implement `--azurefiles-max-stream-size`
- remove arbitrary sleep on Mkdir
- implement `--header-upload`
- implement read and write MimeType for objects
- implement optional methods
    - About
    - Copy
    - DirMove
    - Move
    - OpenWriterAt
    - PutStream
- finish documentation
- disable build on plan9 and js

Fixes #365
Fixes #7378

bin/make_manual.py

@@ -58,6 +58,7 @@ docs = [
     "memory.md",
     "netstorage.md",
     "azureblob.md",
+    "azurefiles.md",
     "onedrive.md",
     "opendrive.md",
     "oracleobjectstorage.md",