OCaml library : Runtime_events.Callbacks

`sig
type t
val create :
?runtime_begin:(int ->
Runtime_events.Timestamp.t ->
Runtime_events.runtime_phase -> unit) ->
?runtime_end:(int ->
Runtime_events.Timestamp.t ->
Runtime_events.runtime_phase -> unit) ->
?runtime_counter:(int ->
Runtime_events.Timestamp.t ->
Runtime_events.runtime_counter -> int -> unit) ->
?alloc:(int -> Runtime_events.Timestamp.t -> int array -> unit) ->
?lifecycle:(int ->
Runtime_events.Timestamp.t ->
Runtime_events.lifecycle -> int option -> unit) ->
?lost_events:(int -> int -> unit) -> unit -> Runtime_events.Callbacks.t
val add_user_event :
'a Runtime_events.Type.t ->
(int ->
Runtime_events.Timestamp.t -> 'a Runtime_events.User.t -> 'a -> unit) ->
Runtime_events.Callbacks.t -> Runtime_events.Callbacks.t
end`