New Example - App to store data locally using SQlite (#102)

* Added files of save data locally using sqlite example App

* Update README.md

save_data_locally_with_sqlite/lib/database/database_queries.dart

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+import 'package:save_data_locally_with_sqlite/database/local_database.dart';
+import 'package:sqflite/sqflite.dart';
+
+Future<void> InsertData(String note, String datetime) async {
+  Database? db = await LocalDatabase.instance.database;
+
+  await db!.rawQuery('''
+  INSERT INTO data (datetime,note,timestamp) VALUES ('$datetime','$note',CURRENT_TIMESTAMP)
+  ''');
+}
+
+Future<List<Map>> GetData() async {
+  Database? db = await LocalDatabase.instance.database;
+  List<Map> list = await db!.rawQuery('''
+  SELECT * FROM data ORDER BY timestamp DESC
+  ''');
+  return list;
+}
+
+Future<void> DeleteData(String datetime) async {
+  Database? db = await LocalDatabase.instance.database;
+  await db!.rawQuery('''
+  DELETE FROM data WHERE datetime='$datetime' 
+  ''');
+}

save_data_locally_with_sqlite/lib/database/local_database.dart

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+import 'dart:async';
+import 'dart:io';
+
+import 'package:path/path.dart';
+import 'package:path_provider/path_provider.dart';
+import 'package:sqflite/sqflite.dart';
+
+class LocalDatabase {
+  static final _databaseName = "database.db";
+  static final _databaseVersion = 1;
+
+  static Database? _database;
+
+  LocalDatabase._privateConstructor();
+  static final LocalDatabase instance = LocalDatabase._privateConstructor();
+
+  Future<Database?> get database async {
+    if (_database != null)
+      return _database; //if database already present it return the database else create a new one then return it
+    _database = await _initDatabase();
+    return _database;
+  }
+
+  _initDatabase() async {
+    Directory documentsDirectory = await getApplicationDocumentsDirectory();
+    String path = join(documentsDirectory.path, '$_databaseName');
+    return await openDatabase(path, version: _databaseVersion,
+        onCreate: (db, int) async {
+      await db.execute('''
+              CREATE TABLE data (
+              datetime TEXT,
+              note TEXT,
+              timestamp TIMESTAMP
+            )
+           ''');
+    });
+  }
+}