API

- Refactor comments/client id var
- Add basic read endpoint for docs, products, expenses, quotes and invoices

api/v1/require_get_method.php

@@ -7,7 +7,11 @@ if ($_SERVER['REQUEST_METHOD'] !== "GET") {
     exit();
 }
 
-// Wildcard client ID for most SELECT queries
+// Wildcard client ID for most SELECT queries, unless otherwise specified (and allowed)
 if ($client_id == 0) {
-    $client_id = "%";
-}
+    if (isset($_GET['client_id'])) {
+        $client_id = intval($_GET['client_id']);
+    } else {
+        $client_id = "%";
+    }
+}