Tweak the rendering of the bibliography to an unordered list.

Previously, the bibliography entries have been rendered as individual paragraphs. This commit tweaks the rendering to rather use an unstyled, left-aligned, unordered list.

This essentially fixes asciidoctor#76 and relates to asciidoctor/asciidoctor-pdf#1889.

lib/asciidoctor-bibtex/processor.rb

@@ -138,7 +138,11 @@ def replace_bibitem_macros(line)
     #
     # Return an array of texts representing an asciidoc list.
     def build_bibliography_list
+
       result = []
+      result << '[.text-left]'
+      result << '[unstyled]'
+
       @citations.each_with_index do |ref, index|
         result << build_bibliography_item(ref, index)
         result << ''
@@ -170,7 +174,7 @@ def build_bibitem_text(key)
     # Build bibliography text for a given reference
     def build_bibliography_item(key, index = 0)
       index += 1
-      result = ''
+      result = '* '
 
       begin
         cptext = if @biblio[key].nil?