Initial KV API concept

Core/Option/IOptionItem.cs

@@ -0,0 +1,16 @@
+using System.Threading.Tasks;
+
+namespace Kruzya.TelegramBot.Core.Option;
+
+/// <summary>
+/// Allows interact with option related with some chat.
+/// </summary>
+public interface IOptionItem<T>
+{
+    public IOptionKey Key { get; }
+    public T Value { get; set; }
+    public bool IsChanged { get; }
+
+    public Task LoadAsync(IOptionStorageAdapter adapter);
+    public Task SaveAsync(IOptionStorageAdapter adapter);
+}