Merge pull request #10 from yifan-gu/master

fix GET type, delete chunk num
cp2: stuck in upload timeout
fixed resending in timeout
Merge branch 'master' of https://github.com/fengjingchao/peer_server
fix kill_download state change back
Merge branch 'master' of https://github.com/fengjingchao/peer_server
be a little bit more aggressive when entering congestion avoidance