Globalize Jekyll's Filters.

As it stands Jekyll does not globalize it's filters.  So anybody wishing to go
into Jekyll's context to process their own Liquid (say in a plugin) may be taken
aback when they find out that Jekyll's filters are not available.
See: jekyll/jekyll-assets#252.

lib/jekyll/filters.rb

@@ -402,3 +402,7 @@ module Jekyll
     end
   end
 end
+
+Liquid::Template.register_filter(
+  Jekyll::Filters
+)

lib/jekyll/renderer.rb

@@ -52,7 +52,6 @@ module Jekyll
       document.trigger_hooks(:pre_render, payload)
 
       info = {
-        :filters   => [Jekyll::Filters],
         :registers => { :site => site, :page => payload['page'] }
       }