mv main package to cmd folder

Makefile

@@ -7,10 +7,10 @@ GOBUILD=go build -ldflags '-s -w -X "github.com/xjasonlyu/tun2socks/constant.Ver
 all: build
 
 build:
-	$(GOBUILD) -v -tags $(BUILDTAGS) -o $(BINDIR)/$(NAME)
+	cd cmd && $(GOBUILD) -v -tags $(BUILDTAGS) -o $(BINDIR)/$(NAME)
 
 debug:
-	$(GOBUILD) -v -tags $(BUILDTAGS) -race -o $(BINDIR)/$(NAME)
+	cd cmd && $(GOBUILD) -v -tags $(BUILDTAGS) -race -o $(BINDIR)/$(NAME)
 
 clean:
 	rm -rf $(BINDIR)