New section header style.
Fix up a few synopses.
diff --git a/Doc/lib/libzlib.tex b/Doc/lib/libzlib.tex
index 0369507..9dbb16b 100644
--- a/Doc/lib/libzlib.tex
+++ b/Doc/lib/libzlib.tex
@@ -1,7 +1,8 @@
% XXX The module has been extended (by Jeremy) but this documentation
% hasn't been updated completely.
-\section{Built-in Module \module{zlib}}
+\section{\module{zlib} ---
+ Compression and decompression compatible with \program{gzip}.}
\declaremodule{builtin}{zlib}
\modulesynopsis{Low-level interface to compression and decompression