[TASK][DOC] (CHANGELOG): add description of recent major changes

CHANGELOG

@@ -3,4 +3,27 @@ this is <CHANGELOG>
 Recent development in Seitosh (bug fixes, new features, etc)
 ------------------------------------------------------------
 
+19.10.2015 (bfef3205e): Revision of end-user documentation of libstfinv
+
+  The end-user documentation supplied by libstfinv is completely revised. New
+  usage() functions are introduced. Program 'onlinehelp' (source is in
+  libstfinv/tests/onlinehelp.cc) outputs the new texts. soutifu is updated to
+  make use of the new usage functions.
+
+21.09.2015 (66d134190): Bug fix in lisousi
+
+  Trim convolution result to reasonable index range (784484c40).
+
+19.07.2015 (f58ebd580, 088bc064ba): New options for stuplo
+
+  Implement new options for winplot emulation:
+   -py          display positive values only
+   -n1 n        set first sample to plot to n'th sample
+                for each input time series
+   -n2 n        set last sample to plot to n'th sample
+                for each input time series
+                n=0 means: last sample read from file
+   -ra          remove average of each input time series
+
+
 ----- END OF CHANGELOG -----