Add breadcrumbs function, docs and tests

devel/tests/helpers/build_breadcrumbs_empty_path.phpt

@@ -0,0 +1,21 @@
+--TEST--
+buildBreadcrumbs: returns empty array for empty request path (frontpage)
+--FILE--
+<?php
+require '/var/www/app/context.php';
+require '/var/www/app/hooks.php';
+require '/var/www/app/constants.php';
+require '/var/www/app/helpers.php';
+
+$ctx = new Context(
+    contentDir: '/tmp/test_content',
+    templates: new Templates('/tmp/base.php', '/tmp/page.php', '/tmp/list.php'),
+    requestPath: '',
+    hasTrailingSlash: false
+);
+
+$result = buildBreadcrumbs($ctx);
+echo count($result) . "\n";
+?>
+--EXPECT--
+0