Switched from QtHelp to using straight HTML files for help.

This is because AppImage (for linux) is readonly and QtHelp requires
write access. But, HTML files shouldn't.

help/genindex.html

@@ -0,0 +1,31 @@
+
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
+  "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+
+<html xmlns="http://www.w3.org/1999/xhtml">
+  <head>
+    <meta http-equiv="X-UA-Compatible" content="IE=Edge" />
+    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
+    <title>Index</title>
+    <link rel="stylesheet" href="_static/nonav.css" type="text/css" />
+    <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> 
+  </head><body>
+
+    <div class="document">
+      <div class="documentwrapper">
+          <div class="body" role="main">
+            
+
+<h1 id="index">Index</h1>
+
+<div class="genindex-jumpbox">
+ 
+</div>
+
+
+          </div>
+      </div>
+      <div class="clearer"></div>
+    </div>
+  </body>
+</html>