lib: introduce abstract_tree

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
trees: introduce Binary Search Tree

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
trees: introduce Red Black Tree

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
trees: create trees group

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>