Add support for simple type annotations in parser and update llhello sample with a possible new low-level dialect syntax leveraging those annotations

#{
fib <- :n {
  if: n < 2 {
    1
  } else: {
    (fib: n-1) + (fib: n-2)
  }
}

main <- {
  print: (string: (fib: 30)) . "\n"
}

}