Add some chapter introductions (not linked into the LibRef yet)

Doc/lib/filesys.tex

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+\chapter{File and Directory Access}
+\label{filesys}
+
+The modules described in this chapter deal with disk files and
+directories.  For example, there are modules for reading the
+properties of files, manipulating paths in a portable way, and
+creating temporary files.  The full list of modules in this chapter is:
+
+\localmoduletable
+
+% XXX can this be included in the seealso environment? --amk
+Also see section \ref{bltin-file-objects} for a description 
+of Python's built-in file objects.
+
+\begin{seealso}
+    \seemodule{os}{Operating system interfaces, including functions to
+    work with files at a lower level than the built-in file object.} 
+\end{seealso}