Allow set title to function return value

Now it is possible to set `document.title` value to function return value. It is useful if you need to compute title value, not just set it as a string. For example:

	App.Router = Backbone.Router.extend
	  routes:
	    "": "index"

	  titles: 
	    "index": (router, route, params) ->
	      "Index — #{App.projectName}"
	    "default": App.projectName