Changes files for feature26815 and 26816

changes/feature26815

+  o Major features (experimental, library support):
+    - When built with --enable-nss, Tor now uses the NSS library for digests,
+      AES, and pseudorandom numbers. Closes ticket 26815.

changes/feature26816

+  o Major features (experimental, library support):
+    - Tor now has _partial_ support for using the NSS cryptography library in
+      place of OpenSSL.  When Tor is configured with --enable-nss, it will
+      use NSS for several (but not yet all) of its cryptography.  (It still
+      relies on OpenSSL for the rest.)  Eventually, if all goes as planned,
+      "--enable-nss" will produce a version of Tor that does not depend on
+      OpenSSL.  Implements ticket 26816.
+
+      WARNING: This feature is experimental.  Don't use it for real security
+      yet, until the code has had much more review, and more bugs have been
+      shaken out.