trifle: enable ReadN(int) to handle corner cases

opt: lazily allocate memory for ring-buffers

opt: improve several methods of ring-buffer

opt: improve http example

opt: enable the close-on-exec flag for the new file descriptor of epoll

trifle: remove unreachable and useless code

fix: write the last data back before closing connections

opt: Skip event-loop when no data to write

Optimization: make the connection GC happy after a UDP loop

UDP fixs and code opts