Updated API's of read/write cache

caches-0 : direct-mapped (E=1) & write-through

API's :
read/mem : location? -> (heap-value? number?)
write/mem : location? heap-value? -> number?
Fixed many heap-ref/set! to benchmarked version
Major fixes

Added write-back cache model
Moved collectors and caches into their own folder
Updated benchmark runner
Save metrics result into .rktd file
Ignored all compiled racket files