Replace text at bkm with plots.

[trekonom]

Hey David,

inspired by this recent post on SO this PR add two new convenience functions

• Add body_replace_gg_at_bkm.
• Add body_replace_plot_at_bkm.

to replace text enclosed in a bookmark with a ggplot or a base r plot.

Both functions are simply adaptions from flextable::body_replace_flextable_at_bkm. As an additional feature I added a keep= parameter to preserve the bookmark.

Best S.

[davidgohel]

thanks @trekonom