Allow docs path to be configured in config.json

This helps when integrating daux.io within a larger project using Bower where we want to keep our docs outside of the daux.io directory and want to keep our filepath changes isolated to the config file rather than modifying index.php.

docs/config.json

@@ -1,6 +1,7 @@
 {
 	"title": "DAUX.IO",
 	"tagline": "The Easiest Way To Document Your Project",
+	"docs_path": "docs",
 	"image": "img/app.png",
 	"theme": "navy",
 	"date_modified": true,

index.php

@@ -66,7 +66,7 @@ software, even if advised of the possibility of such damage.
 require_once('libs/functions.php');
 
 $options = get_options();
-$tree = get_tree("docs", $base_url);
+$tree = get_tree($options['docs_path'], $base_url);
 $homepage_url = homepage_url($tree);
 $docs_url = docs_url($tree);