lib: intro `program_is_in_path`

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
inkscape_tools: detect if inkscape is installed

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: intro the sendmail module

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