Add support for relative path in 'out' & 'paths' options

This PR solves the following issues:

* [x]  If `out` options isn't provided, use target-name appended with `.js` as `out`.
* [x] `paths` & `out` paths can be relative to the `baseUrl`, resolve them before starting the compilation.

``` javascript
grunt.initConfig({
	'requirejs' : {
		"options": {
			"baseUrl": "public",
			"paths": {
				"partials": "../build/templates",
				"templates": "../build/templates",
				"styles": "../build/styles"
			}
		},
		"app": {
			"options": {
				"out": "../build/app.min.js"
			}
		}
	}
});
```