Generate Rules.md and md###.md files from metadata, improve Parameters documentation by referencing schema.

doc/md024.md

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+# MD024 - Multiple headings with the same content
+
+Tags: headers, headings
+
+Aliases: no-duplicate-header, no-duplicate-heading
+
+Parameters:
+
+* `allow_different_nesting`: Only check sibling headings (`boolean`, default `false`)
+* `siblings_only`: Only check sibling headings (`boolean`, default `false`)
+
+This rule is triggered if there are multiple headings in the document that have
+the same text:
+
+```markdown
+# Some text
+
+## Some text
+```
+
+To fix this, ensure that the content of each heading is different:
+
+```markdown
+# Some text
+
+## Some more text
+```
+
+If the parameter `siblings_only` (alternatively `allow_different_nesting`) is
+set to `true`, heading duplication is allowed for non-sibling headings (common
+in changelogs):
+
+```markdown
+# Change log
+
+## 1.0.0
+
+### Features
+
+## 2.0.0
+
+### Features
+```
+
+Rationale: Some Markdown parsers generate anchors for headings based on the
+heading name; headings with the same content can cause problems with that.