CCBool: Add functions if_then and if_then_else

[BridgeTheMasterBuilder]

Just some cute boolean combinators.

Example usage:

[true;false;true;false;true] |> List.filter_map (Bool.if_then (Fun.const 1));;
- : int list = [1; 1; 1]

[true;false;true;false;true] |> List.map (Bool.if_then_else (Fun.const 1) (Fun.const 0));;
- : int list = [1; 0; 1; 0; 1]

let t () = print_endline "Yes" in
let f () = print_endline "No" in
let select = Bool.if_then_else t f in
select true;
select false;;
Yes
No
- : unit = ()

etc.

[c-cube]

Thank you :)