I have posted a new version with some improvements.
The most noticeable is the ability to display multiple images and texts on the same slide.
This was achieved without complicate too much the use of file cataloque (_slidecatalog.txt)
To use multiple images, simply indicate the name of the file one after the other on separate lines.
To separate texts of one slide, use a line that begins with the = character between each text.
Comments and blank lines are allowed inside a slide
To separate two slides, use blank lines and / or comments
It is possible to suppress the display of the command device (* key by default) to have more room on screen and continue to scroll through the slideshow by pressing a button (+ key by default)
Of course, the picture above is not an example of good presentation, but demonstrates the possibilities of the plugin.
The resizing buttons are now barely visible in normal mode but have been expanded to be used anyway.
In Design mode you can not miss them.
In the design mode a red frame identifies the image or selected text on which the positioning commands (small triangles) will be applied. To select a text or image, just click on it. For example, image and text selected here have the same position (relative to the center horizontally and to the lower edge of the screen vertically). If the screen is resized or if you look with a different screen size, they remain in the same position one relative to another.
- The configuration file has been renamed (config_slideshow.lua) and allows you to customize the plugin further.
- Some bugs have been fixed. Among them the program is more stable when a sound is played.
Although one can always install the plugin with the Lua Edu Tools, it's control panel is a little cumbersome. I have not found a way to hide it without hiding slides as well.
And finally I still do not know the appropriate command line to start a sound file with Linux or McIntosh. Never mind. I think the people concerned will have no difficulty in completing themselves the config_slideshow.lua file to have music with the plugin.
I hope this is the last preversion of this plugin. It is becoming quite large for me.
If it is worthwhile, I might release it very soon.
Slides with texts that use images of previous slides work even if slideshow is scrolled backwards or jumping slides. 
