step towards a mode.  " " and "v" for scrolling down
added backspace and "V" to the possible keys
create directory for the images if not exists.
starting with a possibility to quit the mode

keybindings changed towards compatibility to view-mode.
minor mode reol is working for some cases.

A buffer with font Courier and constant font size looks good with the
reol-mode.
press ? calls describe-mode now.

this is an improvement of the documentation.  further view-mode also has
this.