Initial implementation of Scala-style implicit functions.

[samth]

Following the style of the fancy-app package. Does not handle operators yet, nor does it handle ..

This makes f(_,1) expand to fun(x): f(x,1).

Main design question is the behavior of multiple _ in the application. This PR causes each _ to become a distinct function argument, in order of their appearance. Alternative designs:

• multiple _ all become the same binding
• multiple _ are illegal

[samth]

It's not yet clear to me from the enforestation document (probably just because I don't know the implementation well enough) where I would put similar code to handle _.x or _ + 1.

[samth]

This now handles _.x and _(x).