restructured library manual accordiung to functional group

Doc/lib/liballos.tex

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+\chapter{Generic Operating System Services}
+
+The modules described in this chapter provide interfaces to operating
+system features that are available on (almost) all operating systems,
+such as files and a clock.  The interfaces are generally modelled
+after the \UNIX{} or C interfaces but they are available on most other
+systems as well.  Here's an overview:
+
+\begin{description}
+
+\item[os]
+--- Miscellaneous OS interfaces.
+
+\item[time]
+--- Time access and conversions.
+
+\item[getopt]
+--- Parser for command line options.
+
+\item[tempfile]
+--- Generate temporary file names.
+
+\end{description}