Better rewrite/clean URL handling

- New roots-utils.php file for base functions
- Defined useful constants for dealing with common paths
- Refactored rewrites and clean URLs to be more flexible for non
  standard setups
- Custom scripts handler now deals with plugin scripts correctly
- Fixes #204, #270, #278

inc/roots-utils.php

@@ -0,0 +1,28 @@
+<?
+
+// returns WordPress subdirectory if applicable
+function wp_base_dir() {
+  preg_match('!(https?://[^/|"]+)([^"]+)?!', site_url(), $matches);
+  if (count($matches) === 3) {
+    return end($matches);
+  } else {
+    return '';
+  }
+}
+
+// opposite of built in WP functions for trailing slashes
+function leadingslashit($string) {
+  return '/' . unleadingslashit($string);
+}
+
+function unleadingslashit($string) {
+  return ltrim($string, '/');
+}
+
+function add_filters($tags, $function) {
+  foreach($tags as $tag) {
+    add_filter($tag, $function);
+  }
+}
+
+?>