Add teaser images

_posts/2013-01-11-markup-html-tags-and-formatting.md

@@ -1,5 +1,7 @@
 ---
 title: "Markup: HTML Tags and Formatting"
+header:
+  teaser: "markup-syntax-highlighting-teaser.jpg"
 categories:
   - Markup
 tags:
@@ -10,7 +12,7 @@ tags:
   - markup
 ---
 
-## Headings
+A variety of common markup showing how the theme styles them.
 
 # Header one
 

_posts/2013-05-22-markup-more-images.md

@@ -1,6 +1,8 @@
 ---
 title: "Markup: Another Post with Images"
 excerpt: "Examples and code for displaying images in posts."
+header:
+  teaser: "http://farm9.staticflickr.com/8426/7758832526_cc8f681e48_c.jpg"
 tags: 
   - sample post
   - images

_posts/2013-08-16-markup-syntax-highlighting.md

@@ -1,6 +1,8 @@
 ---
 title: "Markup: Syntax Highlighting"
 excerpt: "Post displaying the various ways of highlighting code in Markdown."
+header:
+  teaser: "markup-syntax-highlighting-teaser.jpg"
 tags: 
   - code
   - syntax highlighting