Add asciidoctor gem.

Fixes issue #3506.

Gemfile

@@ -72,6 +72,9 @@ gem "seed-fu"
 gem "redcarpet",     "~> 2.2.2"
 gem "github-markup", "~> 0.7.4", require: 'github/markup'
+# Asciidoc to HTML
+gem  "asciidoctor"
+
 # Servers
 gem "puma", '~> 2.0.1'

Gemfile.lock

@@ -46,6 +46,7 @@ GEM
       rails (~> 3.0)
     addressable (2.3.4)
     arel (3.0.2)
+    asciidoctor (0.1.3)
     awesome_print (1.1.0)
     backports (2.6.7)
     bcrypt-ruby (3.0.1)
@@ -517,6 +518,7 @@ PLATFORMS
 DEPENDENCIES
   acts-as-taggable-on
   annotate!
+  asciidoctor
   awesome_print
   better_errors
   binding_of_caller