restructure to build individual binaries

plugins/repo/Makefile

@@ -1,5 +1,8 @@
 .PHONY: build-in-docker build clean
 
+GO_REPO_ROOT ?= /go/src/github.com/dokku/dokku
+BUILD_IMAGE ?= golang:1.7.1
+
 build-in-docker: clean
 	docker run --rm \
 		-v $$PWD/../..:$(GO_REPO_ROOT) \
@@ -7,8 +10,17 @@ build-in-docker: clean
 		$(BUILD_IMAGE) \
 		bash -c "make build" || exit $$?
 
-build:
-	cd src && go build -a -o ../commands
+build: commands subcommands
+subcommands: subcommands/gc subcommands/purge-cache
+
+commands: **/**/commands.go
+	go build -a -o commands src/commands/commands.go
+
+subcommands/gc: **/**/**/gc.go
+	go build -a -o subcommands/gc src/subcommands/gc/gc.go
+
+subcommands/purge-cache: **/**/**/purge-cache.go
+	go build -a -o subcommands/purge-cache src/subcommands/purge-cache/purge-cache.go
 
 clean:
-	rm -f commands
+	rm -rf commands subcommands