Documenting results from src code archeology.

Kudos to mst for remembering the Writer core comments from Juergen
Pingel.

sw/README

 Writer application code.
+
+Exakt history ist lost before Sept. 18th, 2000, but old source code
+comments show that Writer core dates back until at least November
+1990.

tools/README

-Predates sal - string etc . functions, url manip, stream stuff, polygons, etc.
+Predates sal - string etc . functions, url manip, stream stuff,
+polygons, etc.
+
+Exakt history ist lost before Sept. 18th, 2000, but old source code
+comments show that part of the tools library date back until at least
+April 1991.
+