Improve wording in ChangeLog and documentation

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index a95cc6c..3f144a7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,7 +5,7 @@
 Features
    * Add support for fragmentation of outgoing DTLS handshake messages. This
      is controlled by the maximum fragment length as set locally or negotiated
-     with the peer, as well as new per-connection MTU option, set using
+     with the peer, as well as by a new per-connection MTU option, set using
      mbedtls_ssl_set_mtu().
 
 Bugfix