Makefile tweaks

Re-introduce `make browser` to make a standalone build of `debug.js`
for the web browser.

Makefile

@@ -15,31 +15,31 @@ YARN ?= $(shell which yarn)
 PKG ?= $(if $(YARN),$(YARN),$(NODE) $(shell which npm))
 BROWSERIFY ?= $(NODE) $(BIN)/browserify
 
-.FORCE:
-
 install: node_modules
 
+browser: dist/debug.js
+
 node_modules: package.json
 	@NODE_ENV= $(PKG) install
 	@touch node_modules
 
-lint: .FORCE
-	eslint *.js src/*.js
-
-test-node: .FORCE
-	istanbul cover node_modules/mocha/bin/_mocha -- test/**.js
-
-test-browser: .FORCE
-	mkdir -p dist
-
+dist/debug.js: src/*.js node_modules
+	@mkdir -p dist
 	@$(BROWSERIFY) \
 		--standalone debug \
 		. > dist/debug.js
 
-	karma start --single-run
-	rimraf dist
+lint:
+	eslint *.js src/*.js
 
-test: .FORCE
+test-node:
+	istanbul cover node_modules/mocha/bin/_mocha -- test/**.js
+
+test-browser:
+	$(MAKE) browser
+	karma start --single-run
+
+test:
 	concurrently \
 		"make test-node" \
 		"make test-browser"
@@ -47,4 +47,7 @@ test: .FORCE
 coveralls:
 	cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js
 
+clean:
+	rimraf dist
+
 .PHONY: all install clean distclean