lib/math: intro ceil and floor

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
contrib/inkscape_tools: use floor and ceil to better cut images

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
contrib/inkscape_tools: remove all to_i_strip_e

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
Merge: Fix to inkscape_tools and introduce Float::ceil|floor

Previously image generation would cut off some extremities of the source drawing.

Pull-Request: #426
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>