Creating a reliable TCP client

For this milestone we implemented a basic window.

Our window size is 8.  We keep track of how many packets we have sent
and not received acknowledgements back for (cur_sent).  This number is incremented
on send and decremented on confirmation by an ack from the receiver to
the sender.  We send packets until our cur_sent is the same as window size.
Then we wait for responses and continue the above mentioned process.

TODO:
- Checksum
- Cache complete sent packets in sender
- Cache received packets in a buffer at receiver
  - this only keeps those not in incremental order
- Improved error handling and checking