(ARCHIVE tag): Document C-TAB for forcing cycling of

(ARCHIVE tag): Document C-TAB for forcing cycling of
	archived trees.
	(Checkboxes): Section moved to chapter 5, and extended.
	(The date/time prompt): New section.
	(Link abbreviations): New section.
	(Presentation and sorting): New section.
	(Custom agenda views): Section completely rewritten.
	(Summary): Compare with Planner.
	(Feedback): More info about creating backtraces.
	(Plain lists): Modified example.
	(Breaking down tasks): New section.
	(Custom time format): New section.
	(Time stamps): Document inactive timestamps.
	(Setting tags): More details about fast tag selection.
	(Block agenda): New section.
	(Custom agenda views): Section rewritten.
	(Block agenda): New section.