Medusa System Added

Read about the medusa system [here](https://nadekobot.readthedocs.io/en/latest/medusa/creating-a-medusa/)

src/Nadeko.Medusa/Strings/IMedusaStringsProvider.cs

@@ -0,0 +1,28 @@
+namespace Nadeko.Snake;
+
+/// <summary>
+///     Implemented by classes which provide localized strings in their own ways
+/// </summary>
+public interface IMedusaStringsProvider
+{
+    /// <summary>
+    ///     Gets localized string
+    /// </summary>
+    /// <param name="localeName">Language name</param>
+    /// <param name="key">String key</param>
+    /// <returns>Localized string</returns>
+    string? GetText(string localeName, string key);
+
+    /// <summary>
+    ///     Reloads string cache
+    /// </summary>
+    void Reload();
+
+    // /// <summary>
+    // ///     Gets command arg examples and description
+    // /// </summary>
+    // /// <param name="localeName">Language name</param>
+    // /// <param name="commandName">Command name</param>
+    // CommandStrings GetCommandStrings(string localeName, string commandName);
+    CommandStrings? GetCommandStrings(string localeName, string commandName);
+}