Add function application to Swift's standard library

[anandabits (Matthew Johnson)]

@xwu

This allows the functional operators to have precedence defined only relative to each other; we can require parentheses when they are mixed, for example, with arithmetic operators. This greatly narrows the task of defining appropriate precedence relationships.

That's true, but I think some people would expect functional operators to have lower precedence than basic operators, i.e. 5 + 5 |> takesInt