Update typings

[ktsn]

Update methods option type

Apply this type in the functions of methods option like lifecycle hooks. (Function is alias of (...args: any[]) => any)
We can omit this type annotation for methods option due to this update (See options-test.ts).

Improve $createElement type and expose it

1. Allow to create empty vnode (h()).
2. Allow to pass vnode children to 2nd argument.

Also, this patch enable us to use the type of $createElement. It would be useful when we annotate render option type manually.

import { CreateElement } from 'vue'

export default {
  render (h: CreateElement) {
    // ...
  }
}

[kaorun343]

LGTM.