Create a representation of a section.
A section affects preceding paragraphs or tables; i.e. a section starts at the end of the previous section (or the beginning of the document if no preceding section exists), and stops where the section is declared.
When a new landscape section is needed, it is recommended to add a block_section
type = "continuous", to add the content to be appened in the new section
and finally to add a block_section with
page_size = page_size(orient = "landscape").
section properties defined with function prop_section