Update API

[hajimehoshi]

https://tip.golang.org/pkg/syscall/js/?GOOS=js&GOARCH=wasm

• Now Global, Null and Undefined are functions.
• Add InstanceOf function.

[hajimehoshi]

As Global or other things would be breaking change, my plan is:

1. Make GopherWasm enable to compile with GOARCH=wasm without changing the API first
2. Change the API to be same as syscall/js later

The problem is when to do 2. Whenever I do this, I need to provide advance warning.

[elliott5]

The GopherJS version is around 1Mb smaller if "fmt" is not included, but reflect used instead:

        panic(`fmt.Sprintf("invalid arg: %T", x) ` + reflect.TypeOf(x).String())

[hajimehoshi]

Maybe your point is not related to this issue? But sounds reasonable. I'd be happy if you could send a PR :-)

[hajimehoshi]

Fixed.