Pass anonymous function as a last argument

[alari]

Syntax sugar to simplify the composition.

Without sugar:

func shouldBeAnonymous(x: u32) -> bool:
   true

-- Imagine a complex library function, like onKademliaNeighborhood(key, cb)
func foo(xs: []u32, cb: u32 -> bool):
   for x <- xs:
       cb(x)

func actuallyUsed():
   xs <- Discovery.getXs()
   foo(xs, shouldBeAnonymous)

With sugar:

func foo(xs: []u32, cb: u32 -> bool):
   for x <- xs:
       cb(x)

func actuallyUsed():
   xs <- Discovery.getXs()
   foo(xs) do x: -- x is the local parameter, type is derived from the foo definition
      true

[alari]

Depends on #183