Update CMake documentation (3.21)

lib/docs/filters/cmake/clean_html.rb

@@ -10,6 +10,12 @@ module Docs
           end
         end
 
+        css('section').each do |node|
+          node.children.each do |subnode|
+            node.previous = subnode
+          end
+        end
+
         doc
       end
     end

lib/docs/scrapers/cmake.rb

@@ -13,13 +13,18 @@ module Docs
     options[:title] = false
     options[:root_title] = 'CMake Reference Documentation'
     options[:skip] = %w(release/index.html genindex.html search.html)
-    options[:skip_patterns] = [/\Agenerator/, /\Acpack_gen/, /\Ainclude/, /\Arelease/]
+    options[:skip_patterns] = [/\Agenerator/, /\Acpack_gen/, /\Ainclude/, /\Arelease/, /tutorial\/(\w*%20)+/]
 
     options[:attribution] = <<-HTML
       &copy; 2000&ndash;2021 Kitware, Inc. and Contributors<br>
       Licensed under the BSD 3-clause License.
     HTML
 
+    version '3.21' do
+      self.release = '3.21'
+      self.base_url = "https://cmake.org/cmake/help/v#{self.version}/"
+    end
+
     version '3.20' do
       self.release = '3.20'
       self.base_url = "https://cmake.org/cmake/help/v#{self.version}/"