Update Colorful and add Pow benchmark

tests/ImageSharp.Benchmarks/General/Pow.cs

@@ -0,0 +1,40 @@
+using System;
+using BenchmarkDotNet.Attributes;
+
+namespace SixLabors.ImageSharp.Benchmarks.General
+{
+    public class Pow
+    {
+        [Params(-1.333F, 1.333F)]
+        public float X { get; set; }
+
+
+        [Benchmark(Baseline = true, Description = "Math.Pow 2")]
+        public float MathPow()
+        {
+            float x = this.X;
+            return (float)Math.Pow(x, 2);
+        }
+
+        [Benchmark(Description = "Pow x2")]
+        public float PowMult()
+        {
+            float x = this.X;
+            return x * x;
+        }
+
+        [Benchmark(Description = "Math.Pow 3")]
+        public float MathPow3()
+        {
+            float x = this.X;
+            return (float)Math.Pow(x, 3);
+        }
+
+        [Benchmark(Description = "Pow x3")]
+        public float PowMult3()
+        {
+            float x = this.X;
+            return x * x * x;
+        }
+    }
+}

tests/ImageSharp.Benchmarks/ImageSharp.Benchmarks.csproj

@@ -15,7 +15,7 @@
     <Compile Include="..\ImageSharp.Tests\TestUtilities\TestEnvironment.cs" Link="Tests\TestEnvironment.cs" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="Colourful" Version="1.1.2" />
+    <PackageReference Include="Colourful" Version="1.2.1" />
     <PackageReference Include="System.Numerics.Vectors" Version="4.4.0" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)'=='net461'">