Support export destructured assignment

Choose one: is this a bug report or feature request? Feature request

@GeoffreyBooth I came across an unsupported export syntax that appears to be standard

Input Code

export {foo, bar} = item

Expected Behavior

Should transpile to export var {foo, bar} = item

Current Behavior

Doesn't compile

Possible Solution

Guessing it won't be bad to add this as a supported grammar rule

Context

Not blocking anything, just came across it while working on AST stuff

Environment

• CoffeeScript version:
• Node.js version: