restructured library manual accordiung to functional group

Doc/lib/libstrings.tex

@@ -0,0 +1,20 @@
+\chapter{String Services}
+
+The modules described in this chapter provide a wide range of string
+manipulation operations.  Here's an overview:
+
+\begin{description}
+
+\item[string]
+--- Common string operations.
+
+\item[regex]
+--- Regular expression search and match operations.
+
+\item[regsub]
+--- Substitution and splitting operations that use regular expressions.
+
+\item[struct]
+--- Interpret strings as packed binary data.
+
+\end{description}