Update api.js to improve documentation (#437)

* Update api.js to improve documentation

To resolve #435

* Fix formatting Issues 1

* Fix formatting Issues 2

Author: DavidPratten

src/api.js

@@ -239,8 +239,13 @@ Module["onRuntimeInitialized"] = function onRuntimeInitialized() {
     * You can't instantiate this class directly, you have to use a
     * {@link Database} object in order to create a statement.
     *
-    * **Warning**: When you close a database (using db.close()),
-    * all its statements are closed too and become unusable.
+    * **Warnings**
+    * 1. When you close a database (using db.close()), all
+    * its statements are closed too and become unusable.
+    * 1. After calling db.prepare() you must manually free the assigned memory
+    * by calling Statement.free(). Failure to do this will cause subsequent
+    * 'DROP TABLE ...' statements to fail with 'Uncaught Error: database table
+    * is locked'.
     *
     * Statements can't be created by the API user directly, only by
     * Database::prepare