Restrict MemoryDiagnoserAttribute usage to class (#1122), fixes #1119

* Restrict MemoryDiagnoserAttribute usage to class

* Restricted rest of unrestricted attributes

Author: Rizzen

src/BenchmarkDotNet/Attributes/ArtifactsPathAttribute.cs

@@ -5,6 +5,7 @@
 namespace BenchmarkDotNet.Attributes
 {
     [PublicAPI]
+    [AttributeUsage(AttributeTargets.Class)]
     public class ArtifactsPathAttribute : Attribute, IConfigSource
     {
         public string Value { get; }

src/BenchmarkDotNet/Attributes/DisassemblyDiagnoserAttribute.cs

@@ -4,6 +4,7 @@
 
 namespace BenchmarkDotNet.Attributes
 {
+    [AttributeUsage(AttributeTargets.Class)]
     public class DisassemblyDiagnoserAttribute : Attribute, IConfigSource
     {
         /// <param name="printIL">IL will be printed. False by default.</param>

src/BenchmarkDotNet/Attributes/GroupBenchmarksByAttribute.cs

@@ -5,6 +5,7 @@
 namespace BenchmarkDotNet.Attributes
 {
     [PublicAPI]
+    [AttributeUsage(AttributeTargets.Class)]
     public class GroupBenchmarksByAttribute: Attribute, IConfigSource
     {
         public IConfig Config { get; }

src/BenchmarkDotNet/Attributes/KeepBenchmarkFilesAttribute.cs

@@ -8,6 +8,7 @@ namespace BenchmarkDotNet.Attributes
     /// determines if all auto-generated files should be kept or removed after running the benchmarks
     /// </summary>
     [PublicAPI]
+    [AttributeUsage(AttributeTargets.Class)]
     public class KeepBenchmarkFilesAttribute : Attribute, IConfigSource
     {
         public IConfig Config { get; }

src/BenchmarkDotNet/Attributes/MemoryDiagnoserAttribute.cs

@@ -4,6 +4,7 @@
 
 namespace BenchmarkDotNet.Attributes
 {
+    [AttributeUsage(AttributeTargets.Class)]
     public class MemoryDiagnoserAttribute : Attribute, IConfigSource
     {
         public IConfig Config { get; }

src/BenchmarkDotNet/Attributes/StopOnFirstErrorAttribute.cs

@@ -2,11 +2,13 @@
 using BenchmarkDotNet.Configs;
 using JetBrains.Annotations;
 
-namespace BenchmarkDotNet.Attributes {
+namespace BenchmarkDotNet.Attributes 
+{
     /// <summary>
     /// determines if running should be stop after first error
     /// </summary>
     [PublicAPI]
+    [AttributeUsage(AttributeTargets.Class)]
     public class StopOnFirstErrorAttribute : Attribute, IConfigSource
     {
         public IConfig Config { get; }