Add ability to exclude paths from BTR discovery

[tomdye]

Enhancement

Code

Currently you can add paths to btr via a paths array in the dojorc entry. It would be useful if you could also exclude a path. This could be achieved by adding an exclude boolean to the accepted object.

{
    "build-app": {
        "build-time-render": {
            "root": "app",
            "paths": [
                "home", // add this one
                {
                    "path": "feed.xml", // exclude this one
                    "exclude": true
                }
            ]
        }
    }
}