lib: Float is a Comparable

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

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: remove intro of Number in tests

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: move up to_f and to_i in Number

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: intro Number::zero and Number::is_zero

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