Update headers to never have problematic characters in ids, fixes #64, hopefully

config.rb

+require './lib/redcarpet_header_fix'
+
 set :css_dir, 'stylesheets'
 
 set :js_dir, 'javascripts'
@@ -34,3 +36,4 @@ configure :build do
   # Or use a different image path
   # set :http_prefix, "/Content/images/"
 end
+

lib/redcarpet_header_fix.rb

+module RedcarpetHeaderFix
+  def header(text, level, id)
+    clean_id = id.gsub(/[\.]/, '-').gsub(/[^a-zA-Z0-9\-_]/, '')
+    "<h#{level} id='#{clean_id}'>#{text}</h1>"
+  end
+end
+
+require 'middleman-core/renderers/redcarpet'
+Middleman::Renderers::MiddlemanRedcarpetHTML.send :include, RedcarpetHeaderFix