Paths refactor

Using this approach any override can be specified, including the same folders. So you could bundle everything however you like. If no override path is specified it will just default to the pkg.

``` json
{
  "name": "simple-bower",
  "version": "0.0.0",
  "dependencies": {
    "bootstrap": "~2.2.2",
    "prettify": "https://github.com/robdodson/prettify.git"
  },
  "exportsOverride": {
    "bootstrap": {
      "path/to/less": "less/*.less",
      "path/to/js": "js/*.js"
    },
    "prettify": {
      "path/to/less": "prettify.css",
      "path/to/js": "prettify.js"
    }
  }
}
```