Repaired multiple typos and stuff, WIP on ch. 23
Reformulated nested friends handling and added (r)begin/end members to string
Processed Francesco's feedback for ch. 22
Repaired multiple typos
Processed Francesco's remarks until Ch. 21 (22 next)
Avoiding extra blank before ti(...) macros
removed the parameter pack requirement fm perfect forwarding
making pre2 version
Removed extra blanks around ...