libraries-and-tools.md: add C++ client package
libraries-and-tools.md: add C++ client package

plasticbox/etcd,insequent/etcd,a-robinson/etcd,armstrongli/etcd,fanminshi/etcd,glevand/coreos--etcd,tguangch/etcd,luxas/etcd,a-robinson/etcd,sebrandon1/etcd,plasticbox/etcd,jlamillan/etcd,dannysauer/etcd,handsomesun/etcd,glevand/coreos--etcd,jonboulle/etcd,insequent/etcd,rnaveiras/etcd,OyTao/etcd_learning,xiang90/etcd,mqliang/etcd,akauppi/etcd,CrazyJvm/etcd,akauppi/etcd,ravigadde/etcd,glycerine/etcd,sinsharat/etcd,mickep76/etcd,tguangch/etcd,rnaveiras/etcd,vimalk78/etcd,qqsun8819/etcd,mickep76/etcd,yudai/etcd,heyitsanthony/etcd,joshix/etcd,etcd-io/etcd,visheshnp/etcd,endocode/etcd,rchicoli/etcd,qqsun8819/etcd,joshix/etcd,bdarnell/etcd,fanminshi/etcd,yudai/etcd,vimalk78/etcd,sebrandon1/etcd,whuwxl/etcd,mkumatag/etcd,ajityagaty/etcd,visheshnp/etcd,luxas/etcd,lumjjb/etcd,li-ang/etcd,handsomesun/etcd,hongchaodeng/etcd,heyitsanthony/etcd,cockroachdb/etcd,lumjjb/etcd,sinsharat/etcd,jonboulle/etcd,bluebreezecf/etcd,ktateish/etcd,rnaveiras/etcd,hongchaodeng/etcd,gyuho/etcd,lorneli/etcd,cockroachdb/etcd,li-ang/etcd,jlamillan/etcd,xiang90/etcd,bluebreezecf/etcd,CrazyJvm/etcd,nekto0n/etcd,bdarnell/etcd,gyuho/etcd,mkumatag/etcd,zaphod-concur/etcd,ajityagaty/etcd,lorneli/etcd,whuwxl/etcd,zaphod-concur/etcd,nekto0n/etcd,OyTao/etcd_learning,YuleiXiao/etcd,YuleiXiao/etcd,ravigadde/etcd,mkumatag/etcd,armstrongli/etcd,glycerine/etcd,mqliang/etcd,endocode/etcd,coreos/etcd,etcd-io/etcd,rchicoli/etcd,mqliang/etcd,coreos/etcd,ktateish/etcd,dannysauer/etcd,ajityagaty/etcd,etcd-io/etcd