* Update CHANGES.
* Fix missing `versionadded` declarations.
* Fix a few linter issues.

This lexer add support for PostgreSQL Explain plan :

https://www.postgresql.org/docs/current/sql-explain.html

This was heavily inspired by Maxence Ahlouche work, thanks to him :
https://github.com/maahl/pg_explain_lexer

Co-authored-by: Jean Abou Samra <jean@abou-samra.fr>

This commit adds a new url field to a lexer, which can be used to link
to the language website, instead of relying on having the link in either
languages.rst or the docstring of the lexer. Additionally, it changes the
languages.rst file to auto-generate the list of lexers from the actual
source code, using the provided URL.

* SQL whitespaces - regarding #1905

* Sqlite prompt ungrouped from trailing space

* sqlite prompt with Explicit trailing whitespace token

* Fix insertion of sqlite trail space token

Improve checks.

* Fix lots of small errors.
* Remove the line length check.
* Add an option to skip lexers with no alias
* Run checks in make check
* Add a new CI target.

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>