mapper, predicate, reducer, and flatMapper in map, filter, reduce, and flatMap provide reference to generator and async generator

[richytong]

updates docs signatures as well

mapper(item any, undefined, ftor Generator) -> resultItem Promise|any
mapper(item any, undefined, ftor AsyncGenerator) -> resultItem Promise|any

predicate(item any, undefined, filt Generator) -> condition Promise|boolean|any
predicate(item any, undefined, filt AsyncGenerator) -> condition Promise|boolean|any

reducer(accumulator any, item any, undefined, fold Generator) -> nextAccumulator Promise|any
reducer(accumulator any, item any, undefined, fold AsyncGenerator) -> nextAccumulator Promise|any

flatMapper(item any, undefined, ftor Generator) -> resultItem Promise|any
flatMapper(item any, undefined, ftor AsyncGenerator) -> resultItem Promise|any