Updating "Gittip" to "Gratipay" in text and links

Gittip changed its name to Gratipay more than a year ago.

Author: Britta

docs/_templates/sidebarintro.html

@@ -10,11 +10,11 @@ <h3>Get Updates</h3>
 
 <h3>Donate</h3>
 <p>
-    If you enjoy this guide, consider supporting the author <a href="https://www.gittip.com/kennethreitz/">on Gittip</a>:
+    If you enjoy this guide, consider supporting the author <a href="https://gratipay.com/~kennethreitz/">on Gratipay</a>:
 </p>
 <p>
   <iframe style="border: 0; margin: 0; padding: 0;"
-      src="https://www.gittip.com/kennethreitz/widget.html"
+      src="https://gratipay.com/~kennethreitz/widget.html"
       width="60pt" height="20pt"></iframe>
 </p>
 

docs/_templates/sidebarlogo.html

@@ -10,10 +10,10 @@ <h3>Get Updates</h3>
 
 <h3>Donate</h3>
 <p>
-    If you enjoy this guide, consider supporting the author <a href="https://www.gittip.com/kennethreitz/">on Gittip</a>:
+    If you enjoy this guide, consider supporting the author <a href="https://gratipay.com/~kennethreitz/">on Gratipay</a>:
 </p>
 <p>
   <iframe style="border: 0; margin: 0; padding: 0;"
-      src="https://www.gittip.com/kennethreitz/widget.html"
+      src="https://gratipay.com/~kennethreitz/widget.html"
       width="60pt" height="20pt"></iframe>
-</p>
+</p>