Minor doc fixes.
Minor doc fixes.

Issue #263.

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