Fix for performance degradation. Closes issue #6.
Fix for performance degradation. Closes issue #6.

yaojingwu1992/XlsxWriter,applicationdevm/XlsxWriter,Thhhza/XlsxWriter,seize-the-dave/XlsxWriter,jkyeung/XlsxWriter,jvrsantacruz/XlsxWriter,Thhhza/XlsxWriter,jvrsantacruz/XlsxWriter,seize-the-dave/XlsxWriter,applicationdevm/XlsxWriter,Thhhza/XlsxWriter,jmcnamara/XlsxWriter,mdeemer/XlsxWriter,liukaijv/XlsxWriter,gechong/XlsxWriter,jmcnamara/XlsxWriter,jvrsantacruz/XlsxWriter,gechong/XlsxWriter,yaojingwu1992/XlsxWriter,Thhhza/XlsxWriter,jkyeung/XlsxWriter,applicationdevm/XlsxWriter,liukaijv/XlsxWriter,liukaijv/XlsxWriter,jvrsantacruz/XlsxWriter,mdeemer/XlsxWriter,liukaijv/XlsxWriter,seize-the-dave/XlsxWriter,jmcnamara/XlsxWriter,yaojingwu1992/XlsxWriter,yaojingwu1992/XlsxWriter,jkyeung/XlsxWriter,applicationdevm/XlsxWriter,gechong/XlsxWriter,jkyeung/XlsxWriter,seize-the-dave/XlsxWriter,mdeemer/XlsxWriter,jmcnamara/XlsxWriter,gechong/XlsxWriter,mdeemer/XlsxWriter