Add textilize filter for transforming input into HTML via RedCloth, s…

…o you can have Textile-formatted attributes other than the page's content (for example, an excerpt)

README.textile

@@ -306,6 +306,12 @@ Convert an array into a sentence.
 becomes
 
   foo, bar, and baz
+
+h3. Textilize
+
+Convert a Textile-formatted string into HTML, formatted via RedCloth
+
+  {{ page.excerpt | textilize }}
 
 h3. Include (Tag)
 

lib/jekyll/filters.rb

@@ -1,6 +1,10 @@
 module Jekyll
 
   module Filters
+    def textilize(input)
+      RedCloth.new(input).to_html
+    end
+
     def date_to_string(date)
       date.strftime("%d %b %Y")
     end

test/test_filters.rb

@@ -10,6 +10,10 @@ def setup
     @filter = JekyllFilter.new
   end
 
+  def test_textilize_with_simple_string
+    assert_equal "<p>something <strong>really</strong> simple</p>", @filter.textilize("something *really* simple")
+  end
+
   def test_array_to_sentence_string_with_no_args
     assert_equal "", @filter.array_to_sentence_string([])
   end