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/InsertingDeletingColumns.cs

@@ -0,0 +1,55 @@
+using System;
+using ClosedXML.Excel;
+
+namespace ClosedXML_Examples
+{
+    public class InsertingDeletingColumns : IXLExample
+    {
+        public void Create(String filePath)
+        {
+            var workbook = new XLWorkbook();
+            var ws = workbook.Worksheets.Add("Inserting and Deleting Columns");
+
+            // Range starts with 2 columns
+            var rng = ws.Range("B2:C3"); // Range starts on B2
+
+            // Insert a column before the range
+            ws.Column(1).InsertColumnsAfter(1); // Range starts on C2
+
+            // Insert a column in between the range
+            ws.Column(3).InsertColumnsAfter(1); // Range now has 3 columns
+
+            // Insert a column (from a range) before the range
+            ws.Range("A2:A3").InsertColumnsAfter(1); // Range starts on D2
+
+            // Insert a column (from a range) in between the range
+            ws.Range("D2:D3").InsertColumnsAfter(1); // Range now has 4 columns
+
+            // Inserting columns from a range not covering all columns
+            // does not affect our defined range
+            ws.Range("A1:A2").InsertColumnsAfter(1);
+            ws.Range("E3:E4").InsertColumnsAfter(1);
+
+            // Delete a column before the range
+            ws.Column(1).Delete(); // Range starts on C2
+
+            // Delete a column (from a range) before the range
+            ws.Range("A2:A3").Delete(XLShiftDeletedCells.ShiftCellsLeft); // Range starts on B2
+
+            // Delete a column in between the range
+            ws.Column(3).Delete(); // Range now has 3 columns
+
+            // Delete a column (from a range) in between the range
+            ws.Range("C2:C3").Delete(XLShiftDeletedCells.ShiftCellsLeft); // Range now has 2 columns
+
+            // Deleting columns from a range not covering all columns
+            // does not affect our defined range
+            ws.Range("A1:A2").Delete(XLShiftDeletedCells.ShiftCellsLeft);
+            ws.Range("D3:D4").Delete(XLShiftDeletedCells.ShiftCellsLeft);
+
+            rng.Style.Fill.BackgroundColor = XLColor.Orange;
+
+            workbook.SaveAs(filePath);
+        }
+    }
+}