build: require gcc >= 5.3, boost >= 1.58, openssl >= 1.0.2

This effectively drops support for all versions of Ubuntu older than 16.04

Change-Id: Ie3ab7df9147e97f6467658a6399a4f9379f089c1
Refs: #4462
diff --git a/docs/examples.rst b/docs/examples.rst
index 8689e4f..729a6c5 100644
--- a/docs/examples.rst
+++ b/docs/examples.rst
@@ -52,7 +52,7 @@
 events for execution at specific points of time.
 
 The library internally uses `boost::asio::io_service
-<http://www.boost.org/doc/libs/1_54_0/doc/html/boost_asio/reference/io_service.html>`_ to
+<https://www.boost.org/doc/libs/1_58_0/doc/html/boost_asio/reference/io_service.html>`_ to
 implement fully asynchronous NDN operations (i.e., sending and receiving Interests and
 Data).  In addition to network-related operations, ``boost::asio::io_service`` can be used
 to execute any arbitrary callback within the processing thread (run either explicitly via