ZArchive support (#75)

* ZArchive support

* Fix offset record format

* Simplfiy Extensions

* Delete unused writers and test data

* Rework reader

* Fix build

SabreTools.Data.Extensions.Test/ZArchiveExtensionsTests.cs

@@ -0,0 +1,19 @@
+using SabreTools.Data.Models.ZArchive;
+using SabreTools.Numerics;
+using Xunit;
+
+namespace SabreTools.Data.Extensions.Test
+{
+    public class ZArchiveExtensionsTests
+    {
+        [Fact]
+        public void GetName_Null()
+        {
+            var de = new DirectoryEntry();
+            NameTable nt = new NameTable();
+            string? expected = null;
+            string? actual = de.GetName(nt);
+            Assert.Equal(expected, actual);
+        }
+    }
+}