Add links for ABI/API reports

Author: azat

index.html

@@ -129,6 +129,10 @@ <h3>Documentation</h3>
 <a href="http://www.wangafu.net/~nickm/libevent-2.1/doxygen/html">2.1.x-stable</a>
 <a href="/doc">master</a>
 <br>
+ABI/API compatibility report:
+<a href="https://abi-laboratory.pro/index.php?view=timeline&l=libevent">releases</a>
+<a href="/abi">master</a>
+<br>
 What's new in:
 <a href="https://raw.githubusercontent.com/libevent/libevent/patches-2.0/whatsnew-2.0.txt">2.0.x-stable</a>&ensp;
 <a href="https://raw.githubusercontent.com/libevent/libevent/patches-2.1/whatsnew-2.1.txt">2.1.x-alpha</a>.