pipe operator as in ranges TS

It would be nice to have the same syntax as the ranges TS.

For example, instead of
```
boost::hana::fold(
boost::hana::transform(
boost::hana::values(map)
,func)
,boost::hana::union_)
```
I would write
```
map|boost::hana::values
|boost::hana::transform(func)
|boost::hana::fold(boost::hana::union_)
```

Start by reviewing Hana's existing transform, values, fold, and union_ APIs alongside the ranges TS pipe syntax referenced in the issue. Determine whether the proposed operator can be specified consistently for these operations; done means an agreed design and documented behavior, with compatibility and test scope identified.

Written by the indexing model from the issue text.