Added Chapter 6: Tables/basic-table-structure.html
Added Chapter 6: Tables/table-headings.html
Added Chapter 6: Tables/spanning-columns.html
Added Chapter 6: Tables/spanning-rows.html
Added Chapter 6: Tables/long-tables.html
Added Chapter 6: Tables/width-and-spacing.html
Added Chapter 6: Tables/border-and-background.html
Added Chapter 6: Tables/example.html