Released gnet v1.5.2

#Enhancements

#About poller

By default, gnet utilizes the standard package golang.org/x/sys/unix to implement pollers with epoll or kqueue, where a HASH MAP of fd->conn is introduced to help retrieve connections by file descriptors returned from pollers, but now the user can run go build with build tags poll_opt, like this: go build -tags=poll_opt, and gnet then switch to the optimized implementations of pollers that invoke the system calls of epoll or kqueue directly and add file descriptors to the interest list along with storing the corresponding connection pointers into epoll_data or kevent, in which case gnet can get rid of the HASH MAP of fd->conn and regain each connection pointer by the conversion of void* pointer in the I/O event-looping. In theory, it ought to achieve a higher performance with this optimization.

See #230 for code details.

#About ring-buffer

Adjust the growth strategy of ring-buffer, make it go more smoothly rather than simply doubling up (which may waste a huge amount of memory) in each buffer scaling. ccd37f fd8d27