Fixed bugs due to previous change in the builtin-lookup process.
Created basic done-job notification after next command.
Fixed problem with done-job status display after next command's finish.
Handled Ctrl-C.
Fixed bug for `cd`ing to a non-existant dir.
Merge branch 'jobs'

Conflicts:
	psh.py
Wrote questions' answers.
Wrote questions' answer. Attempted to un-zombify children, but didn't
manage to get it to work.
Updated docstring.
Readline utilized!!
Killed producer when consumer is no longer listening.
Basic ^Z handling set up.
Added signal-catching demo file.