modified method signature of download_piece to suit pthread_create.
tested it working with new method signature.
downloads piece in separate thread successfully.
added todo.
completed extract_next_peer. tested compile success.
changed pwp_start to use extract_next_peer method.
removed commented code.
put threading in pwp_start.
working with one new thread but runtime error when multiple new threads.
fixed race condition when logging (to the same log file).
put critical regions around pieces array and added method to check if two peer ids are same.
modified choosing random piece index to take into account peer and inserted critical regions.
fixed compile error when initialising mutexes.
protected access to saved file using mutex.
added code to loop through all threads and starting a new one in place of a completed thread.
one piece may be associated with multiple peers now.
added some comments.
added logging for peer we are about to connect to.
commented out frequent but less useful logging.
Create README.md