make possible do map to configurable paths

```json
{
	"dependencies": {
		"bootstrap": "~3.0.3"
	},

	"install": {
		"base":  "dist/external",
		"path" : {
			"js": "%(key)s/js",
			"css": "%(key)s/css",
			"eot": "%(key)s/fonts",
			"svg": "%(key)s/fonts",
			"ttf": "%(key)s/fonts",
			"woff": "%(key)s/fonts"
		}		
	}
}
```

Will create this output structure:
```
dist/external
    bootstrap/
        js
        css
        fonts
    jquery
        js
```