refactor (SharpZipLib): #249 use nuget package

Author: Patrick Ammann

PdfSharpCore/Pdf.Filters/FlateDecode.cs

@@ -30,8 +30,8 @@
 using System;
 using System.IO;
 using PdfSharpCore.Internal;
-using PdfSharpCore.SharpZipLib.Zip.Compression;
-using PdfSharpCore.SharpZipLib.Zip.Compression.Streams;
+using ICSharpCode.SharpZipLib.Zip.Compression;
+using ICSharpCode.SharpZipLib.Zip.Compression.Streams;
 
 namespace PdfSharpCore.Pdf.Filters
 {

PdfSharpCore/PdfSharpCore.csproj

@@ -38,6 +38,7 @@ PdfSharpCore is a partial port of PdfSharp.Xamarin for .NET Core Additionally Mi
     <Folder Include="Resources\images\" />
   </ItemGroup>
   <ItemGroup>
+    <PackageReference Include="SharpZipLib" Version="1.3.3" />
     <PackageReference Include="SixLabors.ImageSharp" Version="1.0.4" />
     <PackageReference Include="SixLabors.Fonts" Version="1.0.0-beta17" />
   </ItemGroup>