[WIP] Type safe store binding helper

[ktsn]

This PR add a new helper function bindStore (the name may be changed) to create a Vue component that has mapped state/getters/mutations/actions.

The main difference with the existing decorators, the mapped properties/methods can be inferred with its types. It uses the same strategy of vuejs/vuex#1121 which is on going typings improvement of Vuex.

At first, the users should declare module asset types:

// State
export interface CounterState {
  count: number
}

// Getters
// key: getter name
// value: return type of getter
export interface CounterGetters {
  power: number
}

// Mutations
// key: mutation name
// value: payload type of mutation
export interface CounterMutations {
  increment: { amount: number }
}

// Actions
// key: action name
// value: payload type of action
export interface CounterActions {
  incrementAsync: { amount: number, delay: number }
}

Then, create a store-bound component by using bindStore. Make sure you annotate the module types to the function. It can chains some static methods to map module assets on the component:

const Super = bindStore<CounterState, CounterGetters, CounterMutations, CounterActions>()
  .state(['count'])
  .mutations({
    plus: 'increment'
  })
  .create()

Finally, extend the component so that you use typed store assets on the extended component.

class MyComp extends Super {}

const vm = new MyComp({ store })
assert(vm.count === 0)
vm.plus({ amount: 1 })
assert(vm.count === 1)

This should be merged after vuejs/vuex#1121 is released.

fix #2