Merge pull request #78 from johmue/master

added ExcelSheet::colHidden(), ExcelSheet::rowHidden(), ExcelSheet::setColHidden() and ExcelSheet::setRowHidden()
Merge pull request #79 from johmue/master

added ExcelBook::sheetType() and updated PHP documentation
WS
resolved merge conflict with upstream, fixed formatting 4-spaces --> tabs
fixed formatting 4-spaces --> tabs