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/Styles/StyleWorksheet.cs

@@ -0,0 +1,42 @@
+using System;
+using ClosedXML.Excel;
+
+
+namespace ClosedXML_Examples.Styles
+{
+    public class StyleWorksheet : IXLExample
+    {
+        public void Create(String filePath)
+        {
+            var workbook = new XLWorkbook();
+            var ws = workbook.Worksheets.Add("Style Worksheet");
+
+            ws.Style.Font.Bold = true;
+            ws.Style.Font.FontColor = XLColor.Red;
+            ws.Style.Fill.BackgroundColor = XLColor.Cyan;
+
+            // The following cells will be bold and red
+            // because we've specified those attributes to the entire worksheet
+            ws.Cell(1, 1).Value = "Test";
+            ws.Cell(1, 2).Value = "Case";
+
+            // Here we'll change the style of a single cell
+            ws.Cell(2, 1).Value = "Default";
+            ws.Cell(2, 1).Style = XLWorkbook.DefaultStyle;
+
+            // Let's play with some rows
+            ws.Row(4).Style = XLWorkbook.DefaultStyle;
+            ws.Row(4).Height = 20;
+            ws.Rows(5, 6).Style = XLWorkbook.DefaultStyle;
+            ws.Rows(5, 6).Height = 20;
+
+            // Let's play with some columns
+            ws.Column(4).Style = XLWorkbook.DefaultStyle;
+            ws.Column(4).Width = 5;
+            ws.Columns(5, 6).Style = XLWorkbook.DefaultStyle;
+            ws.Columns(5, 6).Width = 5;
+
+            workbook.SaveAs(filePath);
+        }
+    }
+}