Implement requested changes for PR #371

  - Add allure directory clean before all tests in Allure.NUnit.Examples
  - NUnit.Allure.Core.AllureExtensions.AddScreenDiff is back
    and marked as obsolete (it just directly calls
    AllureLifecycle.AddScreenDiff now).
  - Intendation in Allure.SpecFlowPlugin.csproj fixed.

Allure.NUnit.Examples/AllureSetUpFixture.cs

@@ -0,0 +1,17 @@
+using Allure.Net.Commons;
+using NUnit.Allure.Core;
+using NUnit.Framework;
+
+namespace Allure.NUnit.Examples
+{
+    [SetUpFixture]
+    public class AllureSetUpFixture
+    {
+        [OneTimeSetUp]
+        public static void CleanupResultDirectory() =>
+            AllureExtensions.WrapSetUpTearDownParams(
+                AllureLifecycle.Instance.CleanupResultDirectory,
+                "Clear Allure Results Directory"
+            );
+    }
+}

Allure.NUnit/Core/AllureExtensions.cs

@@ -1,10 +1,9 @@
 using System;
-using System.Reflection;
+using System.ComponentModel;
 using System.Runtime.CompilerServices;
+using System.Threading.Tasks;
 using Allure.Net.Commons;
 using NUnit.Framework.Internal;
-using System.Linq;
-using System.Threading.Tasks;
 
 namespace NUnit.Allure.Core
 {
@@ -204,5 +203,17 @@ public static async Task<T> WrapInStepAsync<T>(
                 throw;
             }
         }
+
+        [Obsolete(
+            "Use AllureLifecycle.AddScreenDiff instance method instead to " +
+                "add a screen diff to the current test."
+        )]
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public static void AddScreenDiff(
+            this AllureLifecycle lifecycle,
+            string expected,
+            string actual,
+            string diff
+        ) => lifecycle.AddScreenDiff(expected, actual, diff);
     }
 }

Allure.SpecFlowPlugin/Allure.SpecFlowPlugin.csproj

@@ -3,7 +3,7 @@
     <PropertyGroup>
         <TargetFrameworks>net462;netstandard2.0</TargetFrameworks>
         <LangVersion>11</LangVersion>
-		<Nullable>enable</Nullable>
+        <Nullable>enable</Nullable>
         <PackageId>Allure.SpecFlow</PackageId>
         <Version>2.10-SNAPSHOT</Version>
         <Authors>Alexander Bakanov</Authors>