Updated spill logic to match textbook.

Created by: rosethompson

• Changed name of cache parameter NUMLINES to NUMSETS to better match book.
• Changed name CacheWriteData to WriteData.
• Fixed bug so that wsim can start logging after a given number of instructions.
• Simplified wsim so it automatically figures out if the second parameter is a testsuite or an elf file.
• Updated readme to reflect changes to wsim.
• Got the directory mode wsim working!
• Updated readme.
• Updated spill logic to reflect changes in textbook.