When we scan a library, store the last write time for a file so we can skip page calculation if there were no modifications.

API/Extensions/FileInfoExtensions.cs

@@ -0,0 +1,13 @@
+using System;
+using System.IO;
+
+namespace API.Extensions
+{
+    public static class FileInfoExtensions
+    {
+        public static bool DoesLastWriteMatch(this FileInfo fileInfo, DateTime comparison)
+        {
+            return comparison.Equals(fileInfo.LastWriteTime);
+        }
+    }
+}