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

doc/md012.md

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+# MD012 - Multiple consecutive blank lines
+
+Tags: blank_lines, whitespace
+
+Aliases: no-multiple-blanks
+
+Parameters:
+
+* `maximum`: Consecutive blank lines (`integer`, default `1`)
+
+Fixable: Most violations can be fixed by tooling
+
+This rule is triggered when there are multiple consecutive blank lines in the
+document:
+
+```markdown
+Some text here
+
+
+Some more text here
+```
+
+To fix this, delete the offending lines:
+
+```markdown
+Some text here
+
+Some more text here
+```
+
+Note: this rule will not be triggered if there are multiple consecutive blank
+lines inside code blocks.
+
+Note: The `maximum` parameter can be used to configure the maximum number of
+consecutive blank lines.
+
+Rationale: Except in a code block, blank lines serve no purpose and do not
+affect the rendering of content.