Trouble shooting
Merge branch 'master' of https://github.com/shiyingzheng/hw10

Conflicts:
	shell.c
Merge branch 'master' of https://github.com/shiyingzheng/hw10
Merge branch 'master' of https://github.com/shiyingzheng/hw10
Merge branch 'master' of https://github.com/shiyingzheng/hw10
Attempts at handling signals and file redirection