Fix some invalid HTML in synopsis

doc/synopsis/Makefile

@@ -58,7 +58,7 @@ categories.png: categories.dot
 
 categories-imagemap.html: categories.dot
 	rm -f $@
-	echo '<img src="categories.png" usemap="#categories">' > $@
+	echo '<img src="categories.png" usemap="#categoriesmap" alt="RGL categories">' > $@
 	dot -Tcmapx $^ >> $@
 
 api-examples.gfs: api-examples.txt MkExx.hs

doc/synopsis/categories.dot

@@ -1,5 +1,5 @@
 
-digraph categories {
+digraph categoriesmap {
 
 size = "11,11" ;
 node [href="#\N"];

doc/synopsis/template.html

@@ -43,7 +43,7 @@ $endfor$
 $if(title)$
     <header id="title-block-header">
       <a href="$rel-root$" title="Home">
-        <img src="$rel-root$/doc/Logos/gf1.svg" height="200px" class="float-md-right ml-3 mb-3 bg-white" alt="GF Logo">
+        <img src="$rel-root$/doc/Logos/gf1.svg" height="200" class="float-md-right ml-3 mb-3 bg-white" alt="GF Logo">
       </a>
       <h1 class="title">$title$</h1>
 $if(subtitle)$
@@ -113,8 +113,7 @@ $endif$
       </div>
 
       <div class="col-6 col-sm-3">
-        <h6 class="text-muted">Contribute</i>
-        </h6>
+        <h6 class="text-muted">Contribute</h6>
         <ul class="list-unstyled">
           <li><a href="http://groups.google.com/group/gf-dev">Mailing List</a></li>
           <li><a href="https://github.com/GrammaticalFramework/gf-core/issues">Issue Tracker</a></li>
@@ -129,8 +128,8 @@ $endif$
         <a href="https://github.com/GrammaticalFramework/gf-rgl">RGL</a> ·
         <a href="https://github.com/GrammaticalFramework/gf-contrib">Contributions</a>
       </div>
-    <div>
-  <div>
+    </div>
+  </div>
 </footer>
 $for(include-after)$
 $include-after$