`type t`
`val create : ?enabled:bool -> ?total:int -> ?unbounded:bool -> label -> t`

`create "barname"` : create new a progress bar labelled "barname". The progress bar is disabled by default

`val enable : label -> unit`

`enable "barname"` : enable the progress bar with label "barname"

`val disable : label -> unit`

`disable "barname"` : disable the progress bar with label "barname"

`val set_total : t -> int -> unit`

`set_total bar 10` : set the max width of the progress bar to 10 units

`val progress : ?i:int -> t -> unit`

increment the progress bar of `i` units

`val reset : t -> unit`

reset the progress bar

`val available : unit -> label list`

return the labels of all available progress bar