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

doc/md023.md

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+# MD023 - Headings must start at the beginning of the line
+
+Tags: headers, headings, spaces
+
+Aliases: header-start-left, heading-start-left
+
+Fixable: Most violations can be fixed by tooling
+
+This rule is triggered when a heading is indented by one or more spaces:
+
+```markdown
+Some text
+
+  # Indented heading
+```
+
+To fix this, ensure that all headings start at the beginning of the line:
+
+```markdown
+Some text
+
+# Heading
+```
+
+Rationale: Headings that don't start at the beginning of the line will not be
+parsed as headings, and will instead appear as regular text.