update

3-ShellP1/dsh

4-ShellP2/.gitignore

4-ShellP2/bats/assignment_tests.sh

4-ShellP2/bats/student_tests.sh

4-ShellP2/convert.py

4-ShellP2/dragon.bin

4-ShellP2/dragon.c

4-ShellP2/dragon_data.h

4-ShellP2/dsh_cli.c

4-ShellP2/dshlib.c

4-ShellP2/dshlib.h

4-ShellP2/fork-exec-1.png

4-ShellP2/fork-exec-2.png

4-ShellP2/makefile

4-ShellP2/questions.md

4-ShellP2/readme.md