Implement ln's four modes

	// 1) 1 target 1 linkname -- T only works here?
	// * linkname does not exist = link as file
	// * linkname exists = delete, link as file
	// * linkname exists as dir = link as $ln/$targ
	// * linkname exists as dir (-T) = *fail*
	// 2) 1 target 0 linkname -- does this imply T's behaviour?
	// * linkname does not exist = link as $PWD/$targ
	// * linkname exists = delete, link as file
	// * linkname exists as dir = *fail*
	// 3) n targets 1 linkname
	// ! linkname not dir = *fail*
	// -> foreach target
	//    see mode 1 (linkname = $ln/$targ)
	// 4) -t=dir n targets
	// this is mode 3 with dirname specified up front
	//
	// * -f cannot remove dirs
	// * -f cannot link ./file as ./file