Add static method support

[adamuso]

Add support for static methods in classes. Simple as that.

class Test extends Area2D {
  constructor() {
    super()
    Test.test()
  }

  static test() {
    print("static")
  }
}

import { Test } from "./src/Test"

class Foo extends Node { 
  constructor() {
    super()
    Test.test()
  }
}

extends Area2D
class_name Test

func _ready():
  self.test()

static func test():
  print("static")

extends Node
class_name Foo

var Test = load("res://compiled/Test.gd")

func _ready():
  Test.test()

closes #69

[johnfn]

Awesome, thanks!