update changes for 2.6.0

(cherry picked from commit c19745c)

CHANGES

@@ -1,5 +1,29 @@
 Changelog
 
+2.6.0
+
+#667 - remove use of pointers to 32bit values
+
+#666 - Cleaning up cmake and enabled more warnings.
+
+#665 - start using const on internal arguments
+
+#662 - Some srtp_driver fixes
+
+#661 - remove travis reference from README.md
+
+#660 - meson.build: implement mbedtls support
+
+#649 - iv length is constant so set only once
+
+#507 - Add x86 SIMD optimizations to crypto datatypes
+
+#643 - Add a missing typedef for stream list ctx
+
+#641 - cmake: Rename TEST_APPS as LIBSRTP_TEST_APPS option
+
+#640 - cmake: Support configuring as subproject
+
 2.5.0
 
 #636 - Make mbedtls hmac less restrictive in line with RFC and library capabilities