Improve BleUuid API and tests (#62)

* Improve tests

* Fix tests

* More improvements and ToDos

* Final API changes
Add tests

* Update readme

---------

Co-authored-by: Rohit Sangwan <rohitsangwan647@gmail.com>

example/lib/home/home.dart

@@ -1,6 +1,5 @@
 // ignore_for_file: use_build_context_synchronously
 
-import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:universal_ble/universal_ble.dart';
 import 'package:universal_ble_example/data/capabilities.dart';

example/lib/home/widgets/scan_filter_widget.dart

@@ -37,7 +37,7 @@ class _ScanFilterWidgetState extends State<ScanFilterWidget> {
         List<String> services = widget.servicesFilterController.text.split(',');
         for (String service in services) {
           try {
-            serviceUUids.add(BleUuid.parse(service.trim()));
+            serviceUUids.add(BleUuidParser.string(service.trim()));
           } on FormatException catch (_) {
             throw Exception("Invalid Service UUID $service");
           }