log: Add Exit, Exitf etc.
log: Add Exit, Exitf etc.

These are equivalent to Fatal etc. except that they do not dump stacks.
Addresses a common complaint.

golang/glog,snowsnail/glog,aolu11/glog,thomasf/lg,youleiy/glog,chinawebeye/glog,justintung/glog,nckturner/glog,chinanjjohn2012/glog,winxxp/glog,going/glog,hongrich/glog,kubernetes/klog,kubernetes/klog,strangemonad/clog,skia-dev/glog,viki-org/glog,zj8487/glog,michael-berlin/glog,sitano/glog,bruceauyeung/glog