Merge pull request #48 from pandamicro/lua-vm

Using curl_multi_perform in batchDownload, Add getFailedAssets, updateAssets function and improve error handling
Feature #4977: Refactor success callback of Downloader, remove thread pool
Feature #4977: Add compressed key parsing for Asset in Manifest
Feature #4977: Add decompress process in AssetsManager
Feature #4977: Add Error decompress in EventListener
Merge branch 'lua-vm' of https://github.com/dumganhar/cocos2d-x into lua-vm