added check if tested methods are available
added ExcelSheet::rowHidden(), ExcelSheet::colHidden(), ExcelSheet::setRowHidden() and ExcelSheet::setColHidden()
Merge remote-tracking branch 'upstream/master'
updated changelog
Merge pull request #78 from johmue/master

added ExcelSheet::colHidden(), ExcelSheet::rowHidden(), ExcelSheet::setColHidden() and ExcelSheet::setRowHidden()