ease pain of working with nested tuples

This PR makes it easier to work with nested tuples, which arise naturally from combinators on products.

Two facilities are introduced: un-nesting functions (con2 - con10), which un-nest tuples of arity up to 10, so they can be processed by ordinary functions; and a `Tuple` construction operator (`/\`), which is a right-associative binary operator that makes constructing nested tuples much more pleasant (and paves the way for a natural `\/` operator for `Either`, which is the dual of `Tuple`).

Example usage (pointless but shows the round-tripping):

```purescript
con6 MyRecord $ a /\ b /\ c /\ d /\ e /\ f
```