add disjoint-set
update README
update demo
update disjoint-set
Merge branch 'master' of https://github.com/ZhangYou0122/algorithms into ZhangYou0122-master

Conflicts:
	Makefile
update readme.md
adding btree.h
save btree
using basic disk io
add split-child method
save
update btree
update btree
update btree_demo
update btree.h
fixed a leak in btree
update comments for btree
update btree
update btree.h
debuging btree