nitcorn: improve default file listing of `FileServer`

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitcorn: minor fix in the header of the HTML page

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
cpp: add missing annotation declaration

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>