Add option to generate a sitemap.xml file for Google (#178)

* Added option to generate a sitemap.xml file for Google

Signed-off-by: Martin Herbst <mail@mherbst.de>

* Permalink was configured in wrong file

Signed-off-by: Martin Herbst <mail@mherbst.de>

* Added canonical link

Signed-off-by: Martin Herbst <mail@mherbst.de>

404.md

@@ -1,6 +1,8 @@
 ---
 layout: intro
 title: Page not found
+permalink: /404.html
+
 ---
 
 {% include base.html %}

_config.yml

@@ -1,11 +1,14 @@
 # Site settings
-title: openHAB 2
+title: openHAB 2 
 description: Empowering the Smart Home
 baseurl: "" # the subpath of your site, e.g. /blog/
 url: "http://docs.openhab.org" # the base hostname & protocol for your site
 twitter_username: openhab
 github_username:  openhab
-permalink: /404.html
 # Build settings
 markdown: kramdown
 exclude: ["CNAME", "pom.xml", "README.md", "CONTRIBUTING.md"]
+# Additional gems for sitemap generation
+gems:
+  - jekyll-sitemap
+  

_includes/header.html

@@ -16,6 +16,7 @@
 
   <!-- Font -->
   <link href='https://fonts.googleapis.com/css?family=Lato:300,400,700' rel='stylesheet' type='text/css' />
+  <link rel="canonical" href="{{ site.url }}{{ page.url }}" />
 
   <script>
   (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){