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.
      *