Convert `changelog` to markdown format

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Handle EROFS/ETXTBSY as permission denied in `fileAccess` (re #8741)

This extends `System.Posix.Files.`access` to map EROFS & ETXTBSY to
mean permission denied just like EACCESS.

Based on a patch by Alain O'Dea and comments by Duncan Coutts

Authored-by: Alain O'Dea <alain.odea@verafin.com>
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>