Reflect optional struct fields in typescript

[clearloop]

Addressed issue #1988

Rust test file:

use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub struct Fields {
    pub hallo: Option<bool>,
    pub spaceboy: bool,
}

Typescript test file:

import * as wbg from '../pkg/typescript_tests';

const fields: wbg.Fields = { spaceboy: true, free: () => { } };

[clearloop]

Sorry for the late, I got myself some rest last week, with my project blown up...

The latest version has no String checks, I think I probably made it, pleeeaaase check out it!

[alexcrichton]

Thanks!