Add options to configure HTML document title (#154)

* Add option to use site title as HTML document title

* Add configurable title separator character

* Keep old document title behaviour when not using use-site-title

index.html

@@ -2,6 +2,7 @@
 layout: page
 title: My website
 subtitle: This is where I will tell my friends way too much about me
+use-site-title: true
 ---
 
 <div class="posts-list">