1. Moved _plugins into themes/classic/_plugins

I think it's probably better to ship plugins with themes to make it
easier to update them.
2. Improved 'install' rake task and made nicer output

themes/classic/_plugins/haml.rb

@@ -0,0 +1,24 @@
+module Jekyll
+  require 'haml'
+  class HamlConverter < Converter
+    safe true
+    priority :low
+
+    def matches(ext)
+      ext =~ /haml/i
+    end
+
+    def output_ext(ext)
+      ".html"
+    end
+
+    def convert(content)
+      begin
+        engine = Haml::Engine.new(content)
+        engine.render
+      rescue StandardError => e
+          puts "!!! HAML Error: " + e.message
+      end
+    end
+  end
+end