[#604] Add some handy filters

lib/chili_project/liquid.rb

 require 'chili_project/liquid/liquid_ext'
+require 'chili_project/liquid/filters'
 require 'chili_project/liquid/tags'
 
 module ChiliProject

lib/chili_project/liquid/filters.rb

+module ChiliProject
+  module Liquid
+    module Filters
+      def default(input, default)
+        input.to_s.strip.present? ? input : default
+      end
+
+      def strip(input)
+        input.to_s.strip
+      end
+    end
+
+    Template.register_filter(Filters)
+  end
+end