Running slideshow/widescreen and slideshow/fullscreen modules directly

Currently, the only way to control the actual aspect ratio used for #f seems to be extra-linguistically, via the slideshow executable.

I think it would make sense for running a program in #lang slideshow/widescreen or #lang slideshow/fullscreen directly via racket or DrRacket to set the default aspect ratio accordingly. In particular, when using DrRacket to run a module in #lang slideshow/widescreen that incorporates a library slide function with an adaptive aspect ratio, the library slide will currently be in full-screen, which I found surprising.

It might also make sense for running the slideshow executable without an explicit --widescreen or --fullscreen argument to similarly let #lang slideshow/widescreen and #lang slideshow/fullscreen establish the default aspect ratio, though that seems like it would be more complicated to implement.

Start by comparing how #lang slideshow/widescreen and #lang slideshow/fullscreen behave when run via racket or DrRacket, especially for adaptive aspect-ratio slide functions. Then inspect the slideshow executable's --widescreen and --fullscreen entry points. Done means the language modules establish the expected default aspect ratio when run directly, with the executable behavior clarified or updated as appropriate.