Added loop hash table and it's associated build function.

- Added a mechanism to build and store a hash table of all loop start and end locations.
- Added a function which is called at the end of init_() and which builds the hash table by doing a single pass through the BF program.
- Added code in processing_() under the '[' instruction which utilizes the hash table for jumps.
- Still need to add code for utilizing the hash table for loop continuations.