Returns the width, height and
aspect ratio of a flextable in a named list.
The aspect ratio is the ratio corresponding to height/width.
Names of the list are widths, heights and aspect_ratio.
See also
Other functions for flextable size management:
autofit(),
dim.flextable(),
dim_pretty(),
fit_to_width(),
height(),
hrule(),
ncol_keys(),
nrow_part(),
width()
