worksheet/cell_data.rb and worksheet/print_style.rb were separated from worksheet.rb
add tests for replace Worksheet#set_comments_author with Worksheet#comments_author=().
replace Worksheet#set_comments_author with Worksheet#comments_author=(). tests pass.
add tests for replace Worksheet#set_tab_color with Worksheet#tab_color=().
replace Worksheet#set_tab_color with Worksheet#tab_color=(). test pass.
add tests for replace Worksheet#set_zoom with Worksheet#zoom=().
replace Worksheet#set_zoom with Worksheet#zoom=(). test pass.