Opal native with block

native.rb

# Class.new
Foo = Class.new(Bar) do
  def woosh
    :kapow
  end
end

# Native.new
LocalStorage = Native.new(`localStorage`) do
  def [](key)
    `getItem(key)`
  end
  
  def []=(key, value)
    `setItem(key, value)`
  end
end