More cleanup, trying to add unit tests.

diff --git a/obsolete-src/README b/obsolete-src/README
new file mode 100644
index 0000000..db449a4
--- /dev/null
+++ b/obsolete-src/README
@@ -0,0 +1,4 @@
+This directory contains source code that has been in use at some point,
+but not used or needed any more. However, there is a chance that such code
+might be useful for some other use later on, and as such it is still retained
+in a somewhat visible place (not just SCM system version history).