lib: revamp the file API, adding `Path` and `FileStat`

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
contrib/sort_downloads: fix makefile to compile alternative or configured scripts

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

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
contrib/rss_download: add a sample configuration

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