* Fixed issue #63 writing for NULL values using writeRow()
* Added excel.skip_empty INI setting that allows null values to be skipped, if set to 2 the empty strings will be skipped as well
* Added Sheet::setRightToLeft() and Sheet::setRightToLeft() methods that specifies whether the sheet in is "right to left" display mode
* Added Book::isTemplate() and Book::setTemplate() methods for detecting xltx files and converting from xlsx to xltx and vice versa
* Fixed compilation with LibXL 3.5.4
* Added optional scope parameter to setNamedRange()/delNamedRange()/getNamedRange() methods
* Updated getNamedRange()/getIndexRange() methods to retrieve hidden state
* Added parameter to readRow/readCol/read methods that specifiy whether to parse formula or its value.
* Added ExcelBook::packDateValues() method for generating Excel date value
* Added ExcelBook::setPrintArea() method for setting print area
* Fixed parsing of non-numeric formulas inside read() method
* Fixed parameter processing inside ExcelSheet::getVerPageBreak()/getHorPageBreak() methods
* Fixed parameter order inside ExcelSheet::getNamedRange()/getIndexRange() methods
* Fixed return value processing inside ExcelBook::setActiveSheet() method
