v0.9.2

Fixed

• MemPath.open("w") on an existing directory raised nothing and destroyed
  the tree. _open() assigned over whatever was already at the name, so
  MemPath("dir").write_text(...) replaced a directory and everything under
  it with a file — silently, in the class the docs present as the reference
  exemplar for extending this library, and the class used as a mock
  filesystem in tests. It now raises IsADirectoryError, as pathlib does.
  The same guard covers the virtual root for every mode, which used to grow a
  bogus "" key in the backend on "w"/"a".
• A MemPath routed through a file raised TypeError.
  _parent_container() walked ancestors with path not in parent, which on a
  bytearray ancestor evaluates "seg" not in bytearray. That TypeError
  sails past the OSError guard in Stat._st_mode(), so even
  MemPath("file.txt/sub").exists() crashed instead of returning False —
  a routine shape in glob/walk and in mkdir(parents=True). It now raises
  NotADirectoryError naming the offending ancestor.
• Pathname had no __eq__/__hash__, so subclasses compared by
  identity. Every pure subclass that didn't hand-write equality — including
  MemPath, and any downstream class subclassing Path directly — was
  unusable as a dict key or set member, and is_relative_to() (which decides
  via == against freshly built parents) always returned False without
  raising. There is now a default keyed on
  (type(self), tuple(self.segments)). LocalPath, PosixPathname and
  WindowsPathname are unaffected — pathlib.PurePath precedes Pathname in
  their MRO and keeps its own equality — as is Uri, which defines one.
• is_relative_to() normalized a str argument by joining it onto
  self. Pathname used cls(self, other) and Uri used
  Uri(self, _ROOT, other), so Uri("a/b").is_relative_to("a") compared
  against "a/b/a" / "/a" and answered False while
  Uri("a/b").is_relative_to(Uri("a")) answered True — the str and object
  forms of the same call disagreed. Both now parse other standalone, as
  CPython does. The generic side uses self.with_segments(other) so a
  subclass's per-instance state (MemPath's backend) survives the
  normalization. Uri("http://h/a/b").is_relative_to("/a") is still True.
• LocalPath.chown() leaked AttributeError/LookupError on Windows.
  shutil.chown exists there while os.chown does not, so an int id raised
  AttributeError and a name raised a misleading LookupError: no such user
  (with no pwd module, every name misses whether or not the user exists).
  It now raises NotImplementedError, which docs/divergences.md already
  promised and which every other unsupported capability here raises. The
  all-unchanged no-op still succeeds.

Full Changelog: v0.9.1...v0.9.2