Introduce the <function> tag for declaring JavaScript functions

[patrick-steele-idem]

function formatCurrency(value) {
  return '$' + value.toFixed();
}

render()
  <div>Total: ${formatCurrency(10}</div>

[philidem]

I'm not a fan of the render() call in sample above

[philidem]

Also, we will probably need to support functions that get instantiated once and functions that are declared inline (so that you can better utilize function closure for accessing local variables).