v0.7.0

Added (Phase 7b new schemes, optional extras)

• dav:/davs: scheme (pathlib_next.uri.schemes.webdav.DavPath):
  extends HttpPath with WebDAV (RFC 4918) PROPFIND for real stat/listdir
  metadata (replacing HTML-index scraping) and PUT/DELETE/MKCOL/MOVE for
  full read/write access. Requests go to the equivalent http:/https:
  URL; as_uri() still reports dav:/davs:. Reuses the http extra,
  no new dependency. rmdir() is recursive by WebDAV spec, unlike
  pathlib.Path.rmdir()'s "must be empty" contract -- documented, not
  silent.
• s3: scheme (pathlib_next.uri.schemes.s3.S3Path,
  s3://bucket/key/path): read/write/list via boto3. New s3 extra.
  S3 has no real directories -- is_dir() is prefix emulation (any
  object key under "<path>/"), mkdir() creates a zero-byte "<path>/"
  marker object, rmdir() requires no other keys under that prefix.
  rename() uses server-side copy_object+delete_object (same-bucket
  only) instead of the generic download+upload+delete move() fallback.

Full Changelog: v0.6.0...v0.7.0