Implement garbage collector for sockets

[ngosang]

Peer should be destroyed after socket timeout or after several seconds without receiving data.
Now you are only destroying the peer if metadata is received
https://github.com/boramalper/magnetico/blob/master/magneticod/magneticod/__main__.py#L121
in other cases, number of peers (and sockets) increases forever until you reach OS limit and process crash.

[ad-m]

@ngosang , please update issue title to respect content. Mention something like garbage collector for sockets.

[ngosang]

Done

[ad-m]

I think there is a related stack trace:

Traceback (most recent call last):
  File "/home/artur/.local/lib/python3.5/site-packages/magneticod/bittorrent.py", line 77, in on_receivable
    received = self.__socket.recv(8192)
OSError: [Errno 9] Bad file descriptor

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "./magneticod", line 9, in <module>
    load_entry_point('magneticod==0.2.0', 'console_scripts', 'magneticod')()
  File "/home/artur/.local/lib/python3.5/site-packages/magneticod/__main__.py", line 81, in main
    loop()
  File "/home/artur/.local/lib/python3.5/site-packages/magneticod/__main__.py", line 154, in loop
    key.fileobj.on_receivable()
  File "/home/artur/.local/lib/python3.5/site-packages/magneticod/bittorrent.py", line 87, in on_receivable
    self.when_error()
  File "/home/artur/.local/lib/python3.5/site-packages/magneticod/__main__.py", line 131, in on_peer_error
    peers[info_hash].remove(peer)
ValueError: list.remove(x): x not in list

[boramalper]

@ad-m It's related to #3, not this one.