convert(): Added parameter "autoclose", which should be a sequence of

convert():  Added parameter "autoclose", which should be a sequence of
	general identifiers for which closing tags will be omitted
	when SGML is generated.  This can be used to tell the markup
	generator to drop stuff like </para>.  Note that it needs to
	be possible for the closing tag to *always* be omitted for it
	to be included in "autoclose".

main():  Added command-line option "-a" / "--autoclose" to set the
	list of general identifiers passed to the convert() function
	as the "autoclose" parameter.  The list may only be specified
	once (not additive) and GIs should be comma-separated.  The
	default list includes only "para".