Lots of new stuff for "module synopsis support." Public interface consists

Lots of new stuff for "module synopsis support."  Public interface consists
of three macros, one which replaces some of the current conventions used in
the module sections:

  \declaremodule:  Requires two parameters: module type (standard, builtin,
	extension), and the module name.  An optional parameter should be
	given as the basis for the module's "key" used for linking to or
	referencing the section.  The "key" should only be given if the
	module's name contains underscores, and should be the name with the
	underscore's stripped.  This should be the first thing after the
	\section used to introduce the module.

  \modulesynopsis:  Requires a single parameter: a short, one-liner
	description of the module that can be used as part of the chapter
	introduction.  This should probably be placed just after the
	\declaremodule, but may be placed anywhere in the same section.

  \localmoduletable:  No parameters.  If a .syn file exists for the current
	chapter (or for the entire document in howto docs), a synopsistable
	is created with the contents loaded from the .syn file.

Some re-organization due to module synopsis support.

Some \def's changed to \newcommand's.