Added a sorting mechanism to emulate how windows sorts files. Refactored cache to support chapter folders as well.

API.Tests/Services/StringLogicalComparerTest.cs

@@ -0,0 +1,28 @@
+using System;
+using API.Comparators;
+using Xunit;
+
+namespace API.Tests.Services
+{
+    public class StringLogicalComparerTest
+    {
+        [Theory]
+        [InlineData(
+           new[] {"x1.jpg", "x10.jpg", "x3.jpg", "x4.jpg", "x11.jpg"}, 
+           new[] {"x1.jpg", "x3.jpg", "x4.jpg", "x10.jpg", "x11.jpg"}
+        )]
+
+        public void TestLogicalComparer(string[] input, string[] expected)
+        {
+            NumericComparer nc = new NumericComparer();
+            Array.Sort(input, nc);
+
+            var i = 0;
+            foreach (var s in input)
+            {
+                Assert.Equal(s, expected[i]);
+                i++;
+            }
+        }
+    }
+}