Added some new syscalls to check

- `get_current_directory_name` was checking for a non-existent syscall. 

Added: 
- `execve`

- `kill`: pretty important to check that this didn't fail. Otherwise we have `zombies` D: 

- `access`: In hw3, probably not a nice solution if it was used, but just in case. I know I've used this in the past. Perhaps not successfully and without any error checking. 

- `system`: I imagine we shouldn't be using this in our assignments. As a check that we are not, the instructors can simply see if it is one of the listed syscalls through `checksyscalls.sh`, see if it is at least error checked, then go from there. If you think it is necessary, I can modify `checksyscalls.sh` to include more useful information when `system` is used. For example, "`system` has been used!! Automatic [insert score here]".
edit: checking whether or not `system` is used through macros is another story. It would be something fun to play around with.