Symlink to latest doc & use symlink in index.html

Author: rocky

docs/mathics-latest.pdf

@@ -0,0 +1 @@
+mathics-1.1-dev.pdf

index.html

@@ -53,7 +53,7 @@ <h2>
 
       <!-- <p><a href="http://mathics.github.io/doc/">Browse online</a></p> -->
 
-      <p><a href="docs/mathics-1.1-dev.pdf">Download PDF</a></p>
+      <p><a href="docs/mathics-latest.pdf">Download PDF</a></p>
 
       <h2>
       <a id="support" class="anchor" href="#support" aria-hidden="true"><span class="octicon octicon-link"></span></a>Support</h2>