fix broken links (fixes #23)

index.html

@@ -2,7 +2,9 @@
 <!--
  Copyright (c) 2016 Mikhail Maximov
  vigorous.activity at gmail dot com
- 
+
+ Copyright (c) 2021 Antony Polukhin
+
  Distributed under the Boost Software License,
  Version 1.0. (See accompanying file LICENSE_1_0.txt
  or copy at http://boost.org/LICENSE_1_0.txt)
@@ -10,7 +12,7 @@
 <html>
 <head>
 <meta charset="utf-8">
-<meta http-equiv="refresh" content="0; url=../../doc/html/conversion.html">
+<meta http-equiv="refresh" content="0; url=https://www.boost.org/doc/libs/master/doc/html/conversion.html">
 <title>Boost.Conversion</title>
 <style>
   body {
@@ -26,7 +28,7 @@
 <body>
   <p>
     Automatic redirection failed, please go to
-    <a href="../../doc/html/conversion.html">../../doc/html/conversion.html</a>
+    <a href="https://www.boost.org/doc/libs/master/doc/html/conversion.html">https://www.boost.org/doc/libs/master/doc/html/conversion.html</a>
   </p>
   <p>
     &copy; 2014-2021 Antony Polukhin