added maximum not tested yet
 On branch ch12
	modified:   ch12/binary_search_tree.hpp
typo
 On branch ch12
	modified:   ch12/binary_search_tree.hpp
added several methods
 On branch ch12
	modified:   ch12/main.cpp
Update README
Update binary_search_tree.hpp
rename readme
	deleted:    ch12/README
	new file:   ch12/readme
 On branch ch12
	renamed:    ch12/readme -> ch12/README