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/Ranges/MultipleRanges.cs

@@ -0,0 +1,22 @@
+using System;
+using ClosedXML.Excel;
+
+namespace ClosedXML_Examples
+{
+    public class MultipleRanges : IXLExample
+    {
+        public void Create(String filePath)
+        {
+            var workbook = new XLWorkbook();
+            var ws = workbook.Worksheets.Add("Multiple Ranges");
+            
+            // using multiple string range definitions
+            ws.Ranges("A1:B2,C3:D4,E5:F6").Style.Fill.BackgroundColor = XLColor.Red;
+
+            // using a single string separated by commas
+            ws.Ranges("A5:B6,E1:F2").Style.Fill.BackgroundColor = XLColor.Orange;
+
+            workbook.SaveAs(filePath);
+        }
+    }
+}