Add optional notes argument to new_slide() for attaching speaker notes to a slide. Notes are written into the pptx's notes slide via officer::set_notes().
Add empty content to slides when writing presentation to use auto-numbered slides (see officer:429)
Allow custom locations by using new_location() when calling new_element(). The R2PptxLocation class is now exported. The R2PptxLocation class has slots ph_location_fn (function) and args (list) instead of the location character slot (#8).
R2PptxSlideList improvements (#3)
Added + method to add R2PptxSlideList objects to R2PptxSlideList objects
Added new_slidelist() to create new slide list objects