* cmdline: port to argparse

* cmdline: adapt the argparse help formatter to actually take terminal width into account

* Update based on review feedback.

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

Co-authored-by: Matthäus G. Chajdas <dev@anteru.net>

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>

* Add font and background colors to Style

* Move all styles to get_style_defs, add tests

* Remove hardcoded styles, add special lineno style

* Add styles for special line numbers in tables

* Update noclasses documentation

* Refactor linenos elements and styles, add tests

* Update AUTHORS

* Fix multiple CSS prefixes, add tests

* Remove Python 2 compatibility

* remove 2/3 shims in pygments.util
* update setup.py metadata

* Remove unneeded object inheritance.

* Remove unneeded future imports.

Unittest classes are kept - for now - since py.test is ok with them.
Generator tests had to be switched to pytest parametrized tests.