Changed insertion routine from being thread-based to being node-based -- allows for reuse of nodes when reinserting them into the queue after they have run on the CPU, hence saves us unnecessary mallocing.  Changed ready_queue from being the first thread to being a pointer to the first thread, which simplifies comparisons when inserting nodes into the queue.  Added current_time field to _thread_info_t to support requirements for ordering under SRTF scheduling scheme.  SRTF test inputs produce output that mostly aligns with sample output provided by Anand.  SRTF is now fully implemented, short of miscellaneous tests we may run.  Added new debug symbol, DEBUG_QUEUE, which prints the state of the ready queue in certain places in the code after modifying the queue -- see scheduleme().  Merged add_thread_to_queue() and insert_thread() to eliminate superfluous function calls.