Reorganize Samples

The samples have become unwieldy when running them from a browser. In particular, the drop-down lists are fixed size with no scrolling, and many of them are now just too large. I have moved all the Calculation samples up a level, and broken several categories (Basic, Chart, DateTime, Engineering, Financial, and Reader) into several pieces.

Convert-Online (now found in the Engineering category) had a number of different problems which are now resolved. It is the only member with any significant code change.

samples/Engineering/BESSELK.php

@@ -0,0 +1,26 @@
+<?php
+
+use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+
+require __DIR__ . '/../../Header.php';
+
+$category = 'Engineering';
+$functionName = 'BESSELK';
+$description = 'Returns the modified Bessel function, which is equivalent to the Bessel functions evaluated for purely imaginary arguments';
+
+$helper->titles($category, $functionName, $description);
+
+// Create new PhpSpreadsheet object
+$spreadsheet = new Spreadsheet();
+$worksheet = $spreadsheet->getActiveSheet();
+
+for ($n = 0; $n <= 5; ++$n) {
+    for ($x = 0; $x <= 5; $x = $x + 0.25) {
+        Calculation::getInstance($spreadsheet)->flushInstance();
+        $formula = "BESSELK({$x}, {$n})";
+        $worksheet->setCellValue('A1', "=$formula");
+
+        $helper->log("$formula = " . $worksheet->getCell('A1')->getCalculatedValue());
+    }
+}