(The spreadsheet): Renamed from "Table calculations".

(The spreadsheet): Renamed from "Table calculations".
	Completely reorganized and rewritten.
	(CamelCase links): Section removed.
	(Repeating items): New section.
	(Tracking TODO state changes): New section.
	(Agenda views): Chapter reorganized and rewritten.
	(HTML export): Section rewritten.
	(Tables in arbitrary syntax): New section.
	(Summary): Better feature summary.
	(Activation): Document problem with cut-and-paste of Lisp code
	from PDF files.
	(Visibility cycling): Document indirect buffer use.
	(Structure editing): Document sorting.
	(Remember): Section rewritten.
	(Time stamps): Better description of time stamp types.
	(Tag searches): DOcument regular expression search for tags.
	(Stuck projects): New section.
	(In-buffer settings): New keywods.
	(History and Acknowledgments): Updated description.