Added target="_blank" for certain links to open in new tab (twitter#71)

Added to links to "Join the Flock", "Twitter Engineering", "Logos and other goodies", and "View all on GitHub"

index.html

@@ -25,10 +25,10 @@
       <div id="main" class="grid-1">
         <div id="logo"><h1>Twitter Open Source</h1></div>
         <h1>Twitter is built on open source software.</h1>
-        <p>Want to help? <a href="https://careers.twitter.com/">Join the Flock</a></p>
-        <p>More about <a href="https://engineering.twitter.com/">Twitter Engineering</a></p>
+        <p>Want to help? <a href="https://careers.twitter.com/" target="_blank">Join the Flock</a></p>
+        <p>More about <a href="https://engineering.twitter.com/" target="_blank">Twitter Engineering</a></p>
         <p>&nbsp;</p>
-        <p><a href="https://brand.twitter.com/">Logos and other goodies</a></p>
+        <p><a href="https://brand.twitter.com/" target="_blank">Logos and other goodies</a></p>
       </div>
 
       <div class="grid grid-3">
@@ -43,7 +43,7 @@ <h1>Statistics</h1>
         </div>
 
         <div id="recently-updated" class="grid-2 omega header">
-          <h1>Recently updated <a href="https://github.com/twitter/repositories">View All on GitHub</a></h1>
+          <h1>Recently updated <a href="https://github.com/twitter/repositories" target="_blank">View All on GitHub</a></h1>
           <ol id="recently-updated-repos"></ol>
         </div>
       </div>