add ChangeLog updates for 3.1.0

ChangeLog

@@ -2,6 +2,29 @@
 Darshan Release Change Log
 --------------------------
 
+Darshan-3.1.0
+=============
+* add stdio I/O library instrumentation module (Philip Carns)
+    - this handles instrumentation of file stream I/O functions
+      like fopen(), fprintf(), fscanf(), etc.
+    - this module also captures stats on the standard streams (stdin,
+      stdout, & stdin)
+* add Lustre instrumentation module (Glenn Lockwood)
+    - this module provides Lustre striping details (e.g., stripe
+      width, stripe size, list of OSTs a file is striped over)
+* add new mmap-based logging mechanism that allows Darshan to
+  generate output logs even in cases where applications don't
+  call MPI_Finalize()
+    - these logs are uncompressed and are per-process rather
+      than per-job
+* add the darshan-merge utility to darshan-util to allow per-process
+  logs generated by the mmap-based logging mechanism to be converted
+  into Darshan's traditional compressed per-job log files
+* augment the POSIX module timestamp counters to also include a
+  LAST_OPEN & FIRST_CLOSE counters to give more details on application
+  I/O intervals
+* avoid saving duplicate mount point entries in Darshan log files
+
 Darshan-3.0.1
 =============
 * bug fix in darshan logutil mount parsing code that was