Initial C# SDK structure and interfaces

Core/ChateniumClient.cs

@@ -0,0 +1,26 @@
+using Chtn.CSharpSDK.Interfaces;
+using System.Net.Http;
+using System;
+
+namespace Chtn.CSharpSDK.Core
+{
+    public class ChateniumClient
+    {
+        private readonly IKeyringAPI _keyring;
+        private readonly IDatabaseAPI _database;
+        private readonly HttpClient _httpClient;
+
+        public ChateniumClient(IKeyringAPI keyring, IDatabaseAPI database)
+        {
+            _keyring = keyring ?? throw new ArgumentNullException(nameof(keyring));
+            _database = database ?? throw new ArgumentNullException(nameof(database));
+
+            _httpClient = new HttpClient();
+            _httpClient.BaseAddress = new Uri("https://api.chatenium.hu");
+        }
+        public void initialize()
+        {
+            _keyring.Set("keyring", "anyad");
+        }
+    }
+}