fix browserify and supply alternative unpkg entry point (closes #606)

Author: Qix-

Makefile

@@ -11,7 +11,7 @@ dist: dist/debug.js dist/test.js
 .INTERMEDIATE: dist/debug.es6.js
 dist/debug.es6.js: src/*.js
 	@mkdir -p dist
-	browserify --standalone debug $< > $@
+	browserify --standalone debug . > $@
 
 dist/debug.js: dist/debug.es6.js
 	@mkdir -p dist

package.json

@@ -45,5 +45,6 @@
     "xo": "^0.23.0"
   },
   "main": "./src/index.js",
-  "browser": "./dist/debug.js"
+  "browser": "./src/browser.js",
+  "unpkg": "./dist/debug.js"
 }