Basic tracker is ready

1. server/peer_table.h and server/peer_table.c
2. server/file_table.h and server/file_table.c
3. server/start.c

Thanks Little Ming!

Signed-off-by: Hongyi Jia <Hongyi.Jia.GR@dartmouth.edu>
Signed-off-by: Jiaming Jiang <Jiaming.Jiang.GR@dartmouth.edu>