Set outline settings

[stramunin]

https://libxlsxwriter.github.io/worksheet_8h.html#a9efae5027e762c9a29f6afa547e4b2db

below - for row
right - for column

In these two examples only the rows are outlined

$excel->outlineSettings(
    true, 
    false, // <-- below
    false
);

$excel->outlineSettings(
    true, 
    true, // <-- below
    false
);

In Microsoft Excel these settings can be found (https://support.microsoft.com/en-us/office/outline-group-data-in-a-worksheet-08ce98c4-0063-4d42-8ac7-8278c49e9aff):

[dormadekhin]

@viest, hi!
When will this feature merge to master branch?