this program runs a user created shell

features:
1. executes built in commands such as cd,pwd,echo
2. pwd : considers the running directory as home directory
3. echo: can handle double qoute("")
4. can run executable
5. runs background processes
6. executes shell commands
7. piping
8. redirection
9. piping and redirection
10. multiple commands

run the makefile and then execute