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.

shrinkToFit was not handled in StyleMerger so it was overwritten by the default cell style
StyleManager didn't add the property to the xml if shrinkToFit was used without alignment or text wrap.
Unit test

…efact

Tests
Added 'addOption' to OptionsManagerInterface
Moved 'setColumnWidths' and 'mergeCells' methods to Xlsx Writer implementation since the actual feature only works for Xlsx at the moment

Test + minor fixes/refacts