Custom theme elements

[willgearty]

I feel like this shouldn't be too difficult. Just need a way to pass a list of theme elements to theme().

[willgearty]

Oh, maybe we can accept some theme() object as a parameter, then just add it to the list of ggplot additions?

[willgearty]

Now that coord_geo exists, the focus should be on adding custom theme elements like here: https://github.com/const-ae/ggupset/blob/master/R/theme_combmatrix.R

[willgearty]

Could also do something using this functionality: https://ggplot2.tidyverse.org/reference/register_theme_elements.html

[willgearty]

Looks like this would also be a good way to tweak the font family, etc. of the interval names. See element_text arguments here: https://ggplot2.tidyverse.org/reference/element.html.