code: public <R> ValueTransformer<W,R> mergeMap(Function<? super T, ? extends Publisher<? extends R>> mapper) {
          return unitAnyM(this.transformerStream().map(v->v.mergeMap(mapper)));
      }
docs: /* (non-Javadoc)
  @see com.oath.cyclops.types.MonadicValue#flatMapP(java.util.function.Function)