SharpZipLib replace or update to fix warnings

[pamapa]

SharpZipLib seems to be well maintained, provides a nuget package and the license is MIT. We should use that, iff not wished/possible, we should at least fix the warnings...

build warnings

>PdfSharpCore\PdfSharpCore\SharpZipLib\Zip\Compression\Streams\DeflaterOutputStream.cs(487,21,487,26): warning CS0114: 'DeflaterOutputStream.Close()' hides inherited member 'Stream.Close()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
>PdfSharpCore\PdfSharpCore\SharpZipLib\Zip\Compression\Streams\InflaterInputStream.cs(670,21,670,26): warning CS0114: 'InflaterInputStream.Close()' hides inherited member 'Stream.Close()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
>PdfSharpCore\PdfSharpCore\SharpZipLib\Zip\Compression\Streams\DeflaterOutputStream.cs(487,21,487,26): warning CS0114: 'DeflaterOutputStream.Close()' hides inherited member 'Stream.Close()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
>PdfSharpCore\PdfSharpCore\SharpZipLib\Zip\Compression\Streams\InflaterInputStream.cs(670,21,670,26): warning CS0114: 'InflaterInputStream.Close()' hides inherited member 'Stream.Close()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
>PdfSharpCore\PdfSharpCore\SharpZipLib\Zip\Compression\Streams\DeflaterOutputStream.cs(487,21,487,26): warning CS0114: 'DeflaterOutputStream.Close()' hides inherited member 'Stream.Close()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
>PdfSharpCore\PdfSharpCore\SharpZipLib\Zip\Compression\Streams\InflaterInputStream.cs(670,21,670,26): warning CS0114: 'InflaterInputStream.Close()' hides inherited member 'Stream.Close()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
>PdfSharpCore\PdfSharpCore\SharpZipLib\Zip\Compression\Streams\DeflaterOutputStream.cs(487,21,487,26): warning CS0114: 'DeflaterOutputStream.Close()' hides inherited member 'Stream.Close()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.
>PdfSharpCore\PdfSharpCore\SharpZipLib\Zip\Compression\Streams\InflaterInputStream.cs(670,21,670,26): warning CS0114: 'InflaterInputStream.Close()' hides inherited member 'Stream.Close()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword.

[jafin]

@pamapa sounds good!

There is a readme.txt in the folder:

This code is an excerpt from the SharpZipLib. The code is unmodified except that all classes
are made internal and moved to the namespace PdfSharpCore.SharpZipLib.

It may be a hangover from the former non-netcore version of this lib.

[pamapa]

I will provide a MR...

[m-gallesio]

Note that the old SharpZipLibCode was under a GPL+CE license which does not seem compatible with MIT.
More recent versions of SharpZipLib have been relicensed to MIT, so this update also fixes this inconsistency which is definitely a pro.

[pamapa]

merged -> fixed