Added support for persistent connections (optional and experimental).
Added support for persistent connections (optional and experimental).

nguyenthaihan/predis,stokes3452/predis,quangnguyen90/predis,SecureCloud-biz/predis,dominics/predis,WalterShe/predis,RedisLabs/predis,nrk/predis,gencer/predis,mrkeng/predis,zhangyancoder/predis,dzung2t/predis,vend/predis,CloudSide/predis,lvbaosong/predis,protomouse/predis,johnhelmuth/predis,channelgrabber/predis,RudyJessop/predis,oswaldderiemaecker/predis,SwelenFrance/predis,gopalindians/predis,moria/predis