Initial commit of the ClosedXML library

Establishes the foundational structure, core Excel functionality, and tooling.

- Implements base components for cells, ranges, columns, and rows.
- Integrates a custom calculation engine with a wide range of Excel functions.
- Adds comprehensive support for styling, conditional formatting, data validation, comments, pictures, and charts.
- Configures build setup, project metadata (NuGet), and developer guidelines.
- Includes editor and Git attributes for consistent code style and line endings.

ClosedXML_Examples/Misc/HideSheets.cs

@@ -0,0 +1,63 @@
+using System;
+using ClosedXML.Excel;
+
+
+namespace ClosedXML_Examples.Misc
+{
+    public class HideSheets : IXLExample
+    {
+        #region Variables
+
+        // Public
+
+        // Private
+
+
+        #endregion
+
+        #region Properties
+
+        // Public
+
+        // Private
+
+        // Override
+
+
+        #endregion
+
+        #region Events
+
+        // Public
+
+        // Private
+
+        // Override
+
+
+        #endregion
+
+        #region Methods
+
+        // Public
+        public void Create(String filePath)
+        {
+            var wb = new XLWorkbook();
+            
+            wb.Worksheets.Add("First Hidden").Hide();
+            wb.Worksheets.Add("Visible");
+            wb.Worksheets.Add("Unhidden").Hide().Unhide();
+            wb.Worksheets.Add("VeryHidden").Visibility = XLWorksheetVisibility.VeryHidden;
+            wb.Worksheets.Add("Last Hidden").Hide();
+
+            wb.SaveAs(filePath);
+        }
+
+        // Private
+
+        // Override
+
+
+        #endregion
+    }
+}