Added support for mergeCells, cell height, shrink to fit

Added support for
    mergeCells:
        // mergeCells (B2:G2), you may use CellHelper::getColumnLettersFromColumnIndex() to convert from "B2" to "[1,2]"
	    $writer->mergeCells([1,2], [6, 2]);

    cell height:
        $row->setHeight(30);

    shouldShrinkToFit:
        $style->setShouldShrinkToFit();

These changes are implemented for XLSX as that's what I need and test spout on.

src/Spout/Writer/Common/Creator/Style/StyleBuilder.php

@@ -183,6 +183,17 @@ class StyleBuilder
         return $this;
     }
 
+    /**
+     * Set should shrink to fit
+     * @param boolean $shrinkToFit
+     * @return void
+     */
+    public function setShouldShrinkToFit($shrinkToFit = true)
+    {
+        $this->style->setShouldShrinkToFit($shrinkToFit);
+        return $this;
+    }
+
     /**
      * Returns the configured style. The style is cached and can be reused.
      *

src/Spout/Writer/Common/Entity/Options.php

@@ -20,4 +20,10 @@ abstract class Options
 
     // XLSX specific options
     const SHOULD_USE_INLINE_STRINGS = 'shouldUseInlineStrings';
+
+    // XLSX column widths
+    const COLUMN_WIDTHS = 'columnWidths';
+
+    // XLSX merge cells
+    const MERGE_CELLS = 'mergeCells';
 }

src/Spout/Writer/Common/Entity/Sheet.php

@@ -27,6 +27,9 @@ class Sheet
     /** @var SheetManager Sheet manager */
     private $sheetManager;
 
+    /** @var bool Sheet is started */
+    private $isSheetStarted = false;
+
     /**
      * @param int $sheetIndex Index of the sheet, based on order in the workbook (zero-based)
      * @param string $associatedWorkbookId ID of the sheet's associated workbook
@@ -108,4 +111,23 @@ class Sheet
 
         return $this;
     }
+
+    /**
+     * @return bool isSheetStarted Sheet was started
+     */
+    public function isSheetStarted()
+    {
+        return $this->isSheetStarted;
+    }
+
+    /**
+     * @param bool $isSheetStarted Set if sheet was started
+     * @return Sheet
+     */
+    public function setIsSheetStarted($isSheetStarted)
+    {
+        $this->isSheetStarted = $isSheetStarted;
+
+        return $this;
+    }
 }