Merge pull request #51 from qiniu/develop

inc version number
Merge pull request #54 from qiniu/develop

Release v2.4.3
Merge pull request #58 from qiniu/develop

merge develop to master
Merge pull request #63 from qiniu/develop

merge to master
Merge pull request #66 from qiniu/develop

correct NodeJS to Node.js
update
Merge pull request #71 from lintianzhi/fix/gist_prefix

update
{} -> nil
fix catch return empty
Merge pull request #73 from lintianzhi/feature/kv_to_nil

{} -> nil
Merge pull request #72 from qiniu/develop

Release 6.0.0
fix "global leak detected: i"; use blanket instead of jscoverage
use urllib instead of http(s)
add default rpc timeout: one hour
add config for new buff encoding;

fixed: upload image can't set encoding to binary 
添加配置，可以设置buff的编码，修复上传图片等二进制文件，文件编码乱码的问题
fix callback url option in PutPolicy
Merge pull request #78 from lzyzsd/develop

fix callback url option in PutPolicy
Merge pull request #77 from h1bomb/develop

modify 'PutExtra' method :add config for new buff encoding;
Merge pull request #75 from fengmk2/urllib

Using urllib fixed #74
add warning of utf8 keys