a3 - cs201 - shell continuation - 3 weeks - due Feb 25
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overview:
enhance small shell - part 2 (3 weeks)

features:
1.  implement background command - if last char in line has ampersand,
		don't wait.

e.g.,
myshell> ls &

basic idea:
read & character and do not do blocking wait or waitpid command.
If the ampersand is not found - you block.

2. write a small program that you can execute that calls
sleep(3) and waits a random amount of time from 1..10 seconds.
Use this to test the next feature.  Call this program
mysleep.  

3.  modify shell to use waitpid and SIGCHILD signal
	to harvest zombies via signal handler that does
	not block (unless you need to for a particular pid).
	You should be able to deal with case #1, case #2 for both
	blocking and non-blocking processes.

4.  built-in history command 
	use malloc for a linked list of commands.
	You should be able to execute any command in list based
	on   !<number>.  
	E.g.,
	(myshell)% !5
	to print out the fifth command (however calculated - up to
	you).  You should be able to print the history list 
	via a built-in history command.  You should
	keep only the last 10 commands.

5.  optional extra credit:
	If you want to implement a shell redirect (say < or >)
	or even a pipe, 5-10 extra credit points will be available.

Turn-in:
	1. typescript showing tests.
	2. Makefile
	3. all *.c and *.h files

System and library calls:
	1. waitpid(2) (wait(2) actually).
	2. malloc(3), free(3)
	3. sleep(3) 
	4. random(3)
	5. optional: dup2(2)