Plugins: Define IPlugin and IPluginOption interfaces

Il2CppInspector.Common/Plugins/API/V101/IPlugin.cs

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+/*
+    Copyright 2020 Katy Coe - http://www.djkaty.com - https://github.com/djkaty
+
+    All rights reserved.
+*/
+
+/// This is an example for future use of how to create a new backwards-compatible API version
+
+using System.Collections.Generic;
+/*
+namespace Il2CppInspector.PluginAPI.V101
+{
+    /// <summary>
+    /// Core interface that all plugins must implement
+    /// </summary>
+    public interface IPlugin : V100.IPlugin
+    {
+        /// <summary>
+        /// Human-readable version string
+        /// Used for plugin selection and updates
+        /// </summary>
+        public string SoneNewProperty { get; }
+    }
+}
+*/