Prepare 16.2.0 (#555)

* Add empty line to CHANGELOG so extraction works

* Fix a bunch of links

* Prepare 16.2.0
diff --git a/src/OpenSSL/crypto.py b/src/OpenSSL/crypto.py
index 61bddb6..52fcdaf 100644
--- a/src/OpenSSL/crypto.py
+++ b/src/OpenSSL/crypto.py
@@ -680,7 +680,7 @@
         :param issuer: Optional X509 certificate to use as issuer.
         :type issuer: :py:class:`X509`
 
-        .. _extension: https://openssl.org/docs/manmaster/apps/
+        .. _extension: https://www.openssl.org/docs/manmaster/apps/
             x509v3_config.html#STANDARD-EXTENSIONS
         """
         ctx = _ffi.new("X509V3_CTX*")