Add tests to verify rule documentation
user
```ruby
require_relative 'setup_tests'

# Ensures there is documentation for every rule, and that the
# descriptions/tags/etc in the rule match those in the documentation
class TestRuledocs < Minitest::Test
  @@rules = MarkdownLint::RuleSet.load_default

  def setup
    @ruledocs = load_ruledocs
  end

  def load_ruledocs
    rules = {}
    curr_rule = nil
    File.read('../RULES.md').split("\n").each do |l|
      if l.match(/^## (MD\d+) - (.*)$/)
        rules[$1] = { :description => $2, :params => {} }
        curr_rule = $1
      elsif l.match(/^Tags: (.*)$/)
        rules[curr_rule][:tags] = $1.split(',').map{|i| i.strip.to_sym}
      elsif l.match(/^Parameters: (.*)$/)
        rules[curr_rule][:params] = $1.split(',').map{|i| i.strip.to_sym}
      end
    end
    rules
  end

  @@rules.each do |id, r|
    define_method("test_ruledoc_description_#{id}") do
      assert_equal r.description, @ruledocs[id][:description]
    end
    define_method("test_ruledoc_tags_#{id}") do
      assert_equal r.tags, @ruledocs[id][:tags]
    end
    define_method("test_ruledoc_params_#{id}") do
      assert_equal r.params.keys.sort, @ruledocs[id][:params].sort
    end
  end

  def test_ruledoc_for_every_rule
    # (and vice versa)
    assert_equal @@rules.keys, @ruledocs.keys
  end
end
```
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