Refine ch5 posix project

[Pleune]

After being assigned this project, I have made some minor changes to the distributed project files to aid in completion of the project. I feel that these changes would make minor improvements to others who are also assigned this project.

Changes:

• CPU.c to lowercase
• Add default "all" target that builds all schedulers, and make it
  default instead of the clean target
• Reorder Makefile directives to be "more readable"
• Add #include "task.h" in cpu.h
• Add error message when user forgets to specify file on cmd line
  instead of segfaulting
• Use run() function in list.c to keep same format
• Prevent memory leaks in list.c by free()-ing deleted nodes
• Add new make file target to README, and elaborate on the files needed
  to be created
• Remove trailing whitespace from various files