For application of simple UNIX shell

Task Titles: 0. Betty would be proud

1. Simple shell 0.1
2. Simple shell 0.2
3. Simple shell 0.4
4. Simple shell 1.0
5. Simple shell 0.1.1
6. Simple shell 0.2.1
7. Simple shell 0.4.1
8. setenv, unsetenv
9. cd
10. ;
11. && and ||
12. alias
13. Variables
14. Comments
15. File as input