Added a 404 error page; added some more linking between the pages

src/routes/error.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+# error handling routes
+class Destructo < Sinatra::Base
+
+  error 404 do
+    erb :'error/404', locals: {
+      title: 'Page not found'
+    }
+  end
+
+end

src/routes/init.rb

@@ -1,4 +1,5 @@
 # frozen_string_literal: true
 
+require_relative 'error'
 require_relative 'index'
 require_relative 'message'

views/error/404.erb

@@ -0,0 +1,5 @@
+<p>This page does not exist.</p>
+
+<p>If you're looking for a message, it's possible that it has already been viewed and subsequently deleted.</p>
+
+<p>If you would like to send a new message, head <a href="/">back home</a> to get started.</p>

views/index/home.erb

@@ -1,5 +1,7 @@
 <div class="row">
   <div class="columns twelve">
     <p>This is the home page.</p>
+
+    <p><a href="/message/new">Click here</a> to send a new message.</p>
   </div>
 </div>