BatFormat

`sig
val set_formatter_output : 'a BatIO.output -> unit
val formatter_of_output : 'a BatIO.output -> Format.formatter
val std_formatter : Format.formatter
val err_formatter : Format.formatter
val pp_set_formatter_output : Format.formatter -> 'a BatIO.output -> unit
val set_formatter_out_channel : 'a BatIO.output -> unit
val formatter_of_out_channel : 'a BatIO.output -> Format.formatter
val pp_set_formatter_out_channel :
Format.formatter -> 'a BatIO.output -> unit
end`