Merge pull request #5 from yifan-gu/master

almost finishing the sending part, more tests are needed..
rename tcp to tcp_send
tcp_recv
add bitmap; reorg structure
Merge branch 'master' of https://github.com/fengjingchao/peer_server
tcp_recv and tests
prototypes of download and upload
commit before merge
finish roughly 1 to 1 congestion testing
prototypes for timeout checking and packet parsing
make code a little bit more clear
merge
merge with master