Compiled libc.a
Merge branch 'app_develop'

Conflicts:
	os/release/kernel
	os/src/app/cd/cd
	os/src/app/hello/hello
	os/src/app/intro/intro
	os/src/app/ls/ls
	os/src/app/memusage/memusage
	os/src/app/shell/shell
Change grub.cfg