re-tackles #85

This simple 'solution' returns all entries for ``--max 0``.  Now, to
avoid this the logic of ``offset`` and ``max`` needs to become more
complex - unless I am missing an obvious solution.

lib/jekyll/scholar/tags/bibliography.rb

@@ -29,11 +29,7 @@ module Jekyll
           end
         end
 
-        # this also allows for --max {...,-2,-1,0,1,...}
-        if max > -1
-            @max = offset + max - 1
-        end
-        items = items[offset..max]
+        items = items[offset..max] if limit_entries?
 
         bibliography = items.each_with_index.map { |entry, index|
           reference = bibliography_tag(entry, index + 1)

lib/jekyll/scholar/utilities.rb

@@ -27,8 +27,6 @@ module Jekyll
       end
 
       def optparse(arguments)
-        @offset = 0   # set default
-        @max = -1     # set default
         return if arguments.nil? || arguments.empty?
 
         parser = OptionParser.new do |opts|
@@ -141,6 +139,18 @@ module Jekyll
         sort bibliography[query || config['query']]
       end
 
+      def offset
+        @offset ||= 0
+      end
+
+      def max
+        @max.nil? ? -1 : @max + offset - 1
+      end
+
+      def limit_entries?
+        !offset.nil? || !max.nil?
+      end
+
       def sort(unsorted)
         return unsorted if skip_sort?