Simple documentation of the copy_reg module.

Guido, you should probably look at this.  The pickle documentation is out of
date; I don't see anything about the __reduce__() stuff or the
__safe_for_unpickling__ attribute.

Doc/lib/libcopyreg.tex

+\section{Standard Module \sectcode{copy_reg}}
+% Note that the label is a little off; the underscore causes LaTeX to
+% yell & scream.
+\label{module-copyreg}
+\stmodindex{copy_reg}
+
+The \code{copy_reg} module provides support for the
+\code{pickle}\refstmodindex{pickle} and
+\code{cPickle}\refbimodindex{cPickle} modules.  The
+\code{copy}\refstmodindex{copy} module is likely to use this in the
+future as well.  It provides configuration information about object
+constructors which are not classes.  Such constructors may be factory
+functions or class instances.
+
+\renewcommand{\indexsubitem}{(in module copy_reg)}
+
+\begin{funcdesc}{constructor}{object}
+  Declares \var{object} to be a valid constructor.
+\end{funcdesc}
+
+\begin{funcdesc}{pickle}{type, function\optional{, constructor}}
+  Declares that \var{function} should be used as a ``reduction''
+  function for objects of type or class \var{type}.  \var{function}
+  should return either a string or a tuple.  The optional
+  \var{constructor} parameter, if provided, is a callable object which
+  can be used to reconstruct the object when called with the tuple of
+  arguments returned by \var{function} at pickling time.
+\end{funcdesc}

Doc/libcopyreg.tex

+\section{Standard Module \sectcode{copy_reg}}
+% Note that the label is a little off; the underscore causes LaTeX to
+% yell & scream.
+\label{module-copyreg}
+\stmodindex{copy_reg}
+
+The \code{copy_reg} module provides support for the
+\code{pickle}\refstmodindex{pickle} and
+\code{cPickle}\refbimodindex{cPickle} modules.  The
+\code{copy}\refstmodindex{copy} module is likely to use this in the
+future as well.  It provides configuration information about object
+constructors which are not classes.  Such constructors may be factory
+functions or class instances.
+
+\renewcommand{\indexsubitem}{(in module copy_reg)}
+
+\begin{funcdesc}{constructor}{object}
+  Declares \var{object} to be a valid constructor.
+\end{funcdesc}
+
+\begin{funcdesc}{pickle}{type, function\optional{, constructor}}
+  Declares that \var{function} should be used as a ``reduction''
+  function for objects of type or class \var{type}.  \var{function}
+  should return either a string or a tuple.  The optional
+  \var{constructor} parameter, if provided, is a callable object which
+  can be used to reconstruct the object when called with the tuple of
+  arguments returned by \var{function} at pickling time.
+\end{funcdesc}