Improve makefile

It can now build both x-releases and for local os/arch.

Makefile

@@ -1,19 +1,40 @@
+BIN  := bin
+DIST := dist
+
+SRC = $(wildcard drone/*.go)
+RELEASES = $(DIST)/drone_linux_amd64.tar.gz \
+	   $(DIST)/drone_linux_386.tar.gz \
+	   $(DIST)/drone_linux_arm.tar.gz \
+	   $(DIST)/drone_darwin_amd64.tar.gz \
+	   $(DIST)/drone_windows_386.tar.gz \
+	   $(DIST)/drone_windows_amd64.tar.gz
+
+GO = GO15VENDOREXPERIMENT=1 go
+
+install: $(BIN)/drone
+	cp $< $(GOPATH)/bin/
+
+release: $(RELEASES)
 
 deps:
-	cd drone
-	go get -u ./...
-
-build:
-	cd drone
-	go install ./...
+	go get -u ./drone/...
 
 test:
-	cd drone
-	go test ./...
+	$(GO) test ./drone/...
 
 clean:
-	rm -rf bin dist
+	rm -rf $(BIN) $(DIST)
 
-dist:
-	mkdir -p bin dist
-	echo dist
+$(BIN)/drone: $(SRC)
+	$(GO) build -o $@ $(SRC)
+
+.PRECIOUS: $(BIN)/%/drone
+$(BIN)/%/drone: GOOS=$(firstword $(subst _, ,$*))
+$(BIN)/%/drone: GOARCH=$(subst .exe,,$(word 2,$(subst _, ,$*)))
+$(BIN)/%/drone: $(SRC)
+	GOOS=$(GOOS) GOARCH=$(GOARCH) $(GO) build -o $@ $(SRC)
+
+$(DIST)/drone_%.tar.gz: $(BIN)/%/drone
+	mkdir -p $(DIST)
+	tar -cvzf $@ --directory=$(BIN)/$* drone
+	sha256sum $@ > $(DIST)/drone_$*.sha256