TODO

To do list:
- *DONE* change exchange_round so that it takes into account what a node has so 
  that it isn't uploading things it doesn't have
- *DONE*change exchange_round so that it adds finish_piece events to the work 
  queue that handle the transfer of a piece from the want list to the have list
- *DONE*change remove_node so that it finds partial downloads and handles them 
  properly
- *DONE*add if statement to the remove_node scan of the work_queue to make sure
  event[2] is a node_id
- *DONE*change the add_node event so that it can add a seed or a partial
  download
- *DONE*implement interest dictionary
- implement altruism
- implement a reset mechanism for the download capacity of a node (right now 
  remain down gets subtracted from but never reset so eventually it is
  reduced to zero and all downloading stops in the swarm)