export as a function (by default) rather than a string

[chocolateboy]

This is a very handy module, but I always end up wrapping it in a function (for convenience/correctness), which gets tedious:

var path  = require('path');
var $root = require('rootrequire');

function root ($path) {
    return path.join($root, $path);
}

var libPath = root('/path/to/lib');

Exporting it as a string value doesn't allow the function to be attached (in ES5). Exporting it as a String object doesn't play well with console.log. Exporting it as a function allows easy access to both e.g.:

var root  = require('rootrequire'); // function
var $root = require('rootrequire').path; // path

The only downside I can see is that this is a breaking change.