add 'cited' option to bibliography tag

the cited option will limit the bibilography to those entries
which have been previously cited on the same page using the
cite tag.

see #10

lib/jekyll/scholar/tags/bibliography.rb

@@ -9,12 +9,25 @@ module Jekyll
 
         @config = Scholar.defaults.dup
         @bibtex_file, @query = arguments.strip.split(/\s*filter:\s*/)
+        
+        if @bibtex_file == 'cited'
+          @bibtex_file = nil
+          @cited = true
+        end
       end
 
       def render(context)
         set_context_to context
 
-        references = entries.map do |entry|
+        references = entries
+
+        if @cited
+          references = cited_references.map do |key|
+            references.detect { |e| e.key == key }
+          end          
+        end
+
+        references.map! do |entry|
           reference = CiteProc.process entry.to_citeproc, :style => config['style'],
             :locale => config['locale'], :format => 'html'
 

lib/jekyll/scholar/tags/cite.rb

@@ -3,23 +3,27 @@ module Jekyll
 
     class CiteTag < Liquid::Tag
       include Scholar::Utilities
-      
+
       attr_reader :key, :pages
-    
+
       def initialize(tag_name, arguments, tokens)
         super
-        
+
         @config = Scholar.defaults.dup
         @key = arguments.strip.split(/\s+/)[0]
       end
 
       def render(context)
         set_context_to context
+
+        context['cited'] ||= []
+        context['cited'] << key
+
         cite key
       end
-      
+
     end
-    
+
   end
 end
 

lib/jekyll/scholar/utilities.rb

@@ -6,7 +6,7 @@ module Jekyll
     # #site readers
     module Utilities
 
-      attr_reader :bibtex_file, :config, :site, :query
+      attr_reader :bibtex_file, :config, :site, :query, :context
 
       def bibtex_options
         @bibtex_options ||= { :filter => :latex }
@@ -108,8 +108,12 @@ module Jekyll
         content_tag :a, content || href, attributes.merge(:href => href)
       end
 
+      def cited_references
+        context && context['cited'] || []
+      end
+
       def set_context_to(context)
-        @site = context.registers[:site]
+        @context, @site, = context, context.registers[:site]
         config.merge!(site.config['scholar'] || {})
       end