Add 3 top buttons, responsive columns

index.html

@@ -24,9 +24,9 @@
 
 <div class="row">
 
-  <div class="col-sm-3">
+  <div class="col-sm-6 col-md-3 offset-md-1">
     <h2>Use</h2>
-    <a href="download/index.html" class="btn btn-primary mb-3 ">
+    <a href="download/index.html" class="btn btn-primary mb-2">
       <i class="fas fa-download mr-1"></i>
       Download GF
     </a>
@@ -43,15 +43,18 @@
     </ul>
   </div>
 
-  <div class="col-sm-4">
+  <div class="col-sm-6 col-md-4">
     <h2>Learn</h2>
 
+    <a href="lib/doc/synopsis.html" class="btn btn-primary mb-2">
+      <i class="fab fa-readme mr-1"></i>
+      RGL Library Synopsis
+    </a>
     <ul>
-      <li><a href="doc/gf-shell-reference.html">Shell Reference</a></li>
-      <li><a href="lib/doc/synopsis.html">RGL Library Synopsis</a></li>
-      <li><a href="gf-book">The GF Book</a></li>
       <li><a href="doc/tutorial/gf-tutorial.html">Tutorial</a></li>
+      <li><a href="gf-book">The GF Book</a></li>
       <li><a href="doc/gf-refman.html">Reference Manual</a></li>
+      <li><a href="doc/gf-shell-reference.html">Shell Reference</a></li>
       <li><a href="doc/gf-quickstart.html">Quick Start</a></li>
       <li><a href="doc/gf-reference.html">Quick Reference</a></li>
     </ul>
@@ -63,19 +66,17 @@
       <li><a href="doc/gf-lrec-2010.pdf">Library Tutorial</a> <small>[PDF]</small></li>
     </ul>
   </div>
-  <div class="col-sm-4">
+  <div class="col-sm-6 col-md-4">
     <h2>Develop</h2>
-    <h4>GF</h4>
+    <a href="https://github.com/GrammaticalFramework/" class="btn btn-primary mb-2">
+      <i class="fab fa-github mr-1"></i>
+        GF on GitHub
+    </a>
     <ul>
       <li><a href="doc/gf-developers.html">Developers Guide</a></li>
-      <li><a href="https://github.com/GrammaticalFramework/">
-        GF on GitHub
-        <i class="fab fa-github"></i>
-      </a></li>
       <!-- <li><a href="/~hallgren/gf-experiment/browse/">Browse Source Code</a></li> -->
       <li><a href="doc/gf-people.html">Authors</a></li>
     </ul>
-    <h4>Applications</h4>
     <ul>
       <li><a href="http://hackage.haskell.org/package/gf/docs/PGF.html">PGF library API (Haskell runtime)</a></li>
       <li><a href="doc/runtime-api.html">PGF library API (C runtime)</a></li>