Adds unique header creation (#743)

Author: Alyss Noland

config.rb

@@ -1,3 +1,6 @@
+# Unique header generation
+require './lib/unique_head.rb'
+
 # Markdown
 set :markdown_engine, :redcarpet
 set :markdown,
@@ -7,7 +10,8 @@
     prettify: true,
     tables: true,
     with_toc_data: true,
-    no_intra_emphasis: true
+    no_intra_emphasis: true,
+    renderer: UniqueHeadCounter
 
 # Assets
 set :css_dir, 'stylesheets'

lib/unique_head.rb

@@ -0,0 +1,14 @@
+# Unique header generation
+require 'middleman-core/renderers/redcarpet'
+class UniqueHeadCounter < Middleman::Renderers::MiddlemanRedcarpetHTML
+  @@head_count = {}
+  def header(text, header_level)
+    friendly_text = text.parameterize
+    @@head_count[friendly_text] ||= 0
+    @@head_count[friendly_text] += 1
+    if @@head_count[friendly_text] > 1
+      friendly_text += "-#{@@head_count[friendly_text]}"
+    end
+    return "<h#{header_level} id='#{friendly_text}'>#{text}</h#{header_level}>"
+  end
+end