Move the Rust tutorial into a sub-directory

To make room for the C++ version next to it :-)

docs/tutorial/highlight_60.js

@@ -1,59 +0,0 @@
-/* LICENSE BEGIN
-    This file is part of the SixtyFPS Project -- https://sixtyfps.io
-    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
-    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>
-
-    SPDX-License-Identifier: GPL-3.0-only
-    This file is also available under commercial licensing terms.
-    Please contact info@sixtyfps.io for more information.
-LICENSE END */
-
-hljs.registerLanguage("60", function (hljs) {
-  const KEYWORDS = {
-    keyword:
-      'struct export import signal property animate for in if states transitions parent root self',
-    literal:
-      'true false',
-    built_in:
-      'Rectangle Image Text TouchArea Flickable Clip TextInput Window',
-    type:
-      'bool string int float length logical_length duration resource',
-  };
-
-  return {
-    name: 'sixtyfps',
-    aliases: ['60'],
-    case_insensitive: false,
-    keywords: KEYWORDS,
-    contains: [
-      hljs.QUOTE_STRING_MODE,
-      hljs.C_LINE_COMMENT_MODE,
-      hljs.C_BLOCK_COMMENT_MODE,
-      hljs.COMMENT('/\\*', '\\*/', {
-        contains: ['self']
-      }),
-      {
-        className: 'number',
-        begin: '\\b\\d+(\\.\\d+)?(\\w+)?',
-        relevance: 0
-      },
-      {
-        className: 'title',
-        begin: '\\b[_a-zA-Z][_\\-a-zA-Z0-9]* *:=',
-      },
-      {
-        className: 'symbol',
-        begin: '\\b[_a-zA-Z][_\\-a-zA-Z0-9]*(:| *=>)',
-      },
-      {
-        className: 'built_in',
-        begin: '\\b[_a-zA-Z][_\\-a-zA-Z0-9]*!',
-      },
-    ],
-    illegal: /@/
-  };
-});
-
-document
-  .querySelectorAll("code.language-60")
-  .forEach((block) => hljs.highlightBlock(block));