* Extract "is_only_option" method
* Check -L argument to be a "known good" argument

* WIP: Add failing test for a matlab class with properties.

* Add some missing keywords

* Add leading \s* matchers to things above the command form regex, as it tends to swallow keywords otherwise.

* Add support for the special 'properties' block syntax.

* Fix apparent infinite loop when given garbage input.

* Use includes to clean up some of my copypasta.

* Fix negative lookahead when there's more than one space between operators.

* Use Whitespace not Text for spaces; combine adjacent whitespace.

* Add support for declarative property constraints.

pyupgrade is a tool to automatically upgrade syntax for newer versions
of the Python language.

The project has been Python 3 only since
35544e2fc6eed0ce4a27ec7285aac71ff0ddc473, allowing for several cleanups:

- Remove unnecessary "-*- coding: utf-8 -*-" cookie. Python 3 reads all
  source files as utf-8 by default.

- Replace IOError/EnvironmentError with OSError. Python 3 unified these
  exceptions. The old names are aliases only.

- Use the Python 3 shorter super() syntax.

- Remove "utf8" argument form encode/decode. In Python 3, this value is
  the default.

- Remove "r" from open() calls. In Python 3, this value is the default.

- Remove u prefix from Unicode strings. In Python 3, all strings are
  Unicode.

- Replace io.open() with builtin open(). In Python 3, these functions
  are functionally equivalent.

Co-authored-by: Matthäus G. Chajdas <Anteru@users.noreply.github.com>

* introduce and apply rfstringescape

* add unit test for raw f-strings

* add further tests

* fix comment