This has come up a few times, and I see no good reason to catch
and report this error.

Fixes #2193

For the pygmentize command line, this pull request adds detection of true-color support on the terminal and makes that the default formatter. It looks up the COLORTERM environment variable having a value of truecolor or 24bit. If that is the case, it sets the default formatter to use the TerminalTrueColorFormatter.

The COLORTERM environment variable is a convention that has been adopted by some terminals for specifying true-color is supported.

* Allow printing lists as JSON.

* Fix failing tests.

* Address review feedback.

* Don't pretty-print the JSON output.

* 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>

PyPy3 on Windows has a test failure in `test_cmdline:test_outfile()`
when trying to unlink the temporary output file. The root cause is that
`cmdline:inner_main()` does not explicitly close the file that it opens,
and PyPy3 isn't auto-closing the file when `inner_main()` returns.
This prevents the file from being unlinked, and the test case fails.