Batteries user guide : BatNumber.RefOps

`sig
type bat__refops_t
val ( += ) :
BatNumber.RefOps.bat__refops_t Pervasives.ref ->
BatNumber.RefOps.bat__refops_t -> unit
val ( -= ) :
BatNumber.RefOps.bat__refops_t Pervasives.ref ->
BatNumber.RefOps.bat__refops_t -> unit
val ( *= ) :
BatNumber.RefOps.bat__refops_t Pervasives.ref ->
BatNumber.RefOps.bat__refops_t -> unit
val ( /= ) :
BatNumber.RefOps.bat__refops_t Pervasives.ref ->
BatNumber.RefOps.bat__refops_t -> unit
end`