Merge pull request #40 from chipdude/master

limit TCP_NODELAY on server side to persistent connections
mutable and decltype improvements
meh...
fix crash in http_exchange caused by will_close being initialized before http_response resp. will_close is now a function.
fix logic error in http_exchange::will_close
use optional<milliseconds> for timeout values. fixes many cases where timeout was being passed as flags to sendto/recvfrom