Added unit tests, added solution, added travis build

CryptoExchange.Net/Authentication/ApiCredentials.cs

@@ -0,0 +1,27 @@
+using System;
+
+namespace CryptoExchange.Net.Authentication
+{
+    public class ApiCredentials
+    {
+        /// <summary>
+        /// The api key
+        /// </summary>
+        public string Key { get; }
+        /// <summary>
+        /// The api secret
+        /// </summary>
+        public string Secret { get; }
+
+        public ApiCredentials() { }
+
+        public ApiCredentials(string key, string secret)
+        {
+            if(string.IsNullOrEmpty(key) || string.IsNullOrEmpty(secret))
+                throw new ArgumentException("Apikey or apisecret not provided");
+
+            Key = key;
+            Secret = secret;
+        }
+    }
+}