Merge pull request #229 from ideawu/dev

Support very large batch commands
Merge pull request #236 from ideawu/dev

merge dev, Reduce round trip time for single request
Merge pull request #240 from ideawu/dev

Fix bug on ssdb-dump that lose data
Merge pull request #243 from ideawu/dev

merge dev, add zcount, zsum, zavg ... commands
add zsum function

add zsum function
Merge pull request #244 from jiangxixin/master

nodejs api add zsum function