Ability to pass custom Func to CallNode

[Dentrax]

Carry: #277

Motivation

In the current implementation, you can not pass a function to CallNode directly. It’s the only option to pass a func from env; which you need to set Callee field.

Use Case

divFn := func(left, right float64) float64 {
	if right == 0 {
		panic("integer divide by zero")
	}
	return left / right
}

ast.Patch(node, &ast.CallNode{
	Func:    divFn,
	Arguments: []ast.Node{n.Left, n.Right},
})

[antonmedv]

Done! Now CallNode have a Func field.