This enriches the space of recognized builtins.

Note that this also fixes the space after a builtin being included in
the token.

- Add pitch language names to builtins.  They are not highlighted
  specially in the default style, but can be in a custom style.

- Refactor matching of builtins in order to avoid confusion between
  dim chord modifier and \dim dynamic command.

- Support grob subproperties.

- Add segno repeat type.

- While at it, update builtins for latest version.

* LilyPond: update builtins to 2.23.4

* Doc: deduplicate LilyPond in language lists

* Doc: exclude lilypond style from gallery

Because it's specific to LilyPond code and doesn't give good results
on Python code.

* Add lexer and style for LilyPond

GNU LilyPond is a text-based music typesetter. Because its concepts
are completely different from programming languages, this adds
a special-purpose to highlight the special tokens.

The SchemeLexer is expanded to gain the ability of detecting when
one expression stops. LilyPondLexer subclasses SchemeLexer.

Builtins (the most important part) are generated with a script
put in external/ (as was already done for Lasso).

As part of this change, the CPSALexer is made no longer to
inherit from SchemeLexer. The inheritance was unused anyway.

* Fixup: translators names have underscores

* Fixup: avoid duplicate builtins

* Fixup: update goldens

* Fixup: typo

* Fixup: add missing tokens to style

* Fixup: update lexer comments

* Fixup: Tentative style adjustments

* Fixup: move test file to examplefiles/

* Fixup: miscellaneous fixes (to be finished)

* Fixup: escape all braces

* Fixup: use Text, not Whitespace

* Fixup: fixes for lexing and style

* Fixup: update goldens!

* Fixup: also test alist assignments

* Fixup: recognize escape sequences in strings

* Fixup: use Comment.Single

* Fixup: Whitespace, not Text!

* Fixup: fix pitch parsing

* Fixup: update comment

* Fixup: remove redundant re.UNICODE

Although pygmentize -N is much cheaper than file, it makes some bad guesses,
so use file first.

Add support for MIME type application/json.

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>