chore: refactoring some code to introduce a common base class for all api classes

src/Extensions/HttpResponseMessageExtensions.cs

@@ -10,7 +10,7 @@ namespace Novaloop.PaymoApi.Extensions
         {
             if (!response.IsSuccessStatusCode)
             {
-                throw new PaymoApiException((int) response.StatusCode, await response.Content.ReadAsStringAsync());
+                throw new ApiException((int) response.StatusCode, await response.Content.ReadAsStringAsync());
             }
         }
     }